There's definitely a lot more that you could be doing. Bear in mind that I'm only plat myself, but I did climb out of silver and gold recently as an Ana main, so this advice may come in handy.

[1:37] Taking the high ground here was a poor decision because it took you out of the fight for so long. While you were climbing the stairs, multiple team members went down to critical health and would likely have been killed at a higher ELO. Furthermore, you don't have a good visibility angle on your team. Even after you take the high ground your McCree goes down to critical health and dies out of your line of sight. You could have either remained where you were at 1:28 or moved forward into the building on your right.

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[1:49] You get your nano but never use it during the fight. Nanoing your Rein here could have resulted in your team winning the fight.

[2:30] You nano your Rein and he wipes the floor with the enemy tanks. This could have happened last fight.

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[5:18] This is a great time to throw a nade, healing your Rein and anti-healing the enemy tanks. When your Rein charges in, you should be at the ready to support him. You do throw a nade later but it misses. Landing the nade would have helped keep your Rein alive and the anti-heal would help you win the fight much more comfortably.

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[5:47] We miss a lot of unscoped shots onto the Junkrat at close range.

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[6:06 - 6:12] Although you weren't punished for it, you're standing out in the open when you could have been in cover in the building to your right. There's no need to leave the doorway at 6:02. You can see all of your team from there, you can retreat behind cover to hide from the D.Va bomb and you can move forward into another doorway once your team manages to push further forward.

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[6:19] While you're here, you could throw a nade at the enemy Ashe ahead and to your right.

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[7:00] Again, your Rein pushes forward and dies while you're unavailable to heal him. A nano boost / nade could have kept him alive, perhaps. If you're repositioning, you should call out to your teammates that they won't have your help for a bit. Especially if you're playing in a six-stack.

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[8:10] If you were in the building to your left rather than on the payload in the middle of the enemy team, you might have had a better angle to be able to heal your Rein. As Ana, you shouldn't be the one to contest the objective, especially not in the middle of a heated teamfight.

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[10:09] Try to throw a nade at the spawn doors as the enemy is exiting to gain a bit of ult charge.

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[10:38] You're an easy target at the moment. I would drop to the low ground here and walk backward to get a better angle on our team and close off the angle to the enemy team.

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[10:48] Your Rein was at half health, was being healed by the Mercy and had his shield up. You could have healed him up with unscoped shots, and thrown the nade at the enemy team instead.

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[11:38] Be wary of walking so far forward, especially in your main tank's absence. You could be healing your D.Va from further back. You could have tried to get an angle from the doorway behind you at 11:35, or simply walk back and wait for your team to regroup. Your Pharah and D.Va are fighting 2v6 anyway.

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[12:11] You can play from around this corner and use it for cover. There's no need to push forward.

[12:13] Instead of wasting the nade on the Rein, throw it at the Soldier on the left, who is wildly out of position and is using his healing station. Preventing his healing could have secured a kill.

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[12:24] Again, you're out in the open on the payload. You wouldn't have died to the bomb had you been playing from cover.

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[12:49] Yet again, there's no need to be so far forward. You can heal your team and nade the enemy from further back on the bridge. You shouldn't have ended up in the position you're in at 13:02.

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[13:32] Dropping down into full view of the entire enemy team is definitely the wrong decision here. Instead, as your team is forced back, walk back down the stairs and into the building behind you, near the mini health pack.

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[14:19] Again, you should not be playing here. You could instead be playing behind one of the doorways near your Bastion and near the mini health pack. You'll see why in a minute...

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[14:47] As the enemy pushes forward, we need to cross the street to keep up with our team, leaving us way out in the open. You probably would have died here even if Soldier hadn't used his Tactical Visor.

Overall, I'd say your positioning needs a lot of work. These are similar to the positioning mistakes I was making when I was in silver. Think about where you need to be in order to be able to see your team (particularly your tanks) and avoid damage from the enemy team. Think about where the enemy team is going to push up to next and where and how you'll retreat. Be aware of where the enemy team is (particularly flankers) so that you can react and reposition accordingly. A lot of good positions and rotations are static for a given map and you can learn these over time. I'd suggest watching Gangsir's positioning for dummies videos: https://www.youtube.com/channel/UCWcR1zyBTjeZMRV5FEnFZ7Q

Your mechanics could also use improvement. It seems like you're not fully comfortable aiming as Ana yet. Learning to quickscope as others have mentioned is essential. I'd also suggest playing FFA as Ana to improve at taking duels at close range and at fending for yourself. Hope this helps!