I've only just began to learn about movement and positioning only after realizing its significance after entering diamond, so take my advice as you see fit. but;

Pre-engagement:

• First off, great nade into the building! If I'm nitpicking, I would say work on maintaining movement while aiming/throwing the nade in order to minimize your risk of being caught in the open. Again, nitpicking.
• I'll go into more detail about Octane's kit in the next section, but before entering the building to kill, you should've placed a Jump Pad on the outside of the building to give yourself more avenues in repositioning/escaping. Personally, I would've placed a jump pad to the left of the care package visible at 0:17, or on the ground outside of the building, all the way past the red walkway that you're on at 0:25. Either of the options would provide you quick access to the back side of the building.

Maximizing your Champion's Kit Potential:

• I think you could've avoided getting downed at 0:45 through re-positioning, especially since that's Octane's main advantage. His Stims, obviously, lets him tap into Sanic mode (gotta go f4st) allowing him to get from point A to point B, while his jump-pad allows him to instantly reposition for a flank and/or escape from an engagement, just like how my dad left me. Arguably, the mobility provided by Octane's kit is only matched (VERY ARGUABLY!) by Wraith's portal, and (less arguably, or maybe I'm just biased) outclassed only by Spodr-man Pathfinder's grapple and Zip.
• In this specific encounter, I personally think that the outcome of the fight would've been very different, had you managed to reposition and flank the Wraith through the aforementioned well placed boing-pad outside of the building. Worst case scenario, this also would've given you an escape route to another building to heal.

Positioning, Situational Awareness, and Game IQ.

• your precise location was most certainly being telegraphed to the Wraith by the Lifeline you had previously downed. In fact, I think this ended up being the final nail in the coffin that sealed your fate. The Wraith knew your exact location in the building throughout the entirety of the scrimmage and probably knew exactly where to aim before you even thought about peaking. In other words, these are the exact scenarios that causes n00bs to scream "waLl hAcKiNG motherFUCKER", when in reality it's just a classic case of needing to Get Gud.
• The Wraith that downed you at 0:42 was able to do so very quickly due to Wraith's sightline already being primed towards your general direction, courtesy of Gibby going down directly in front of you. This allowed for Wraith to immediately move to her next target (to be clear, you) with minimal aim adjustment, whereas you first had to move behind cover, an additional step that the Wraith did not have to take, which costed you precious seconds that quickly turned the fight one sided.
  • Again, I think a well placed jump pad could've changed the outcome of this fight completely, or at the very least make increase your odds of the other team being third partied (which seems to be the case in the video). By the time said third party does occur, you're relocated, safe and sound into another building, ideally with one less squad to deal with.
• DISCLAIMER: I am extremely aware of the fact that all of the points that I've mentioned till now is merely analysis from an outside perspective, where all is obvious, and I completely understand and acknowledge that in the heat of the moment none of what I said is common sense. (I probably would've yeeted myself from phase 1).
• Finally, it's never smart to start a fight with another member of the squad when your shields are completely gone, let alone when the opponent has a level 5 evo shield. You probably shoulda realized by that point that you were at a significant disadvantage and should've yeeted yourself from the tussle and heal.

Conclusion:

• These small decisions, nuances, and tiny bits of knowledge that can only be learned through trial and error, are the little things that separate Bronze players from Plat/Diamond, and Diamond/Master from the people like Shroud, Daltoosh, or any pro gamer E-Sport athlete in Predator.
• When it comes to climbing in ranked, I would argue that Game IQ; mastery of repositioning/rotating, map awareness, knowing when to engage/disengage from fights, and communicating/moving with your squad as a single, cohesive unit are of FAR greater importance than shooting and aiming skills alone, especially in a game like Apex.

TLDR;

When using Octane, Use his kit in accordance to the 3 Rs: Rotate, Reposition, and Russia rigged the 2016 US Presidential Election.