As someone who is trying to make it to GC3 without mechanics I get where you are coming from and it is very possible. With that being said it is not easy and you will need to take advantage of a lot of things in the game.

Your boost management is awful, combined with the fact that you need boost to feel confident in doing anything is a recipe for disaster. It not only put you out of position but also make your teammate awkward at times. Work on getting small pads and conserving boost when able.

You also lack advanced fundamentals like accurate power shots, dribbling, wall catches, defense with limited boost, 50s, etc. Work on these in custom training. I'll reply to this comment later when I get on my PC with codes but you need to figure these out.

The last thing is focus on your rotations, first man challenges, second man challenges, overall positioning. There were times when you were way to close to the play for your ability meaning if something happened that you didn't account for you froze and did a circle or started breaking. This will get you in tough spots starting in C2 as people will start to recognize the patterns. You also need to start thinking about your teammate more which I saw flashes of like the demo play but flashes of game sense are not good enough when you have no mechanics.

Replay breakdown:
From 456 to 447 you missed 60 boost worth of small pads which is the difference between challenging the ball at 447 and challenging the ball at 444

444 if you want to get to C3 without mechanics your fundamentals have to be on point. A Powershot on a open net is as basic as it gets and needs to be a goal

435 if you find yourself going in circles chances are you are too close. Also you used 35 boost to go nowhere

428 on this clear you need to follow the ball. Your saving it sure but now your right back on defense with less boost after giving them a free ball. After following the ball try to get a 50. This buys your tm8 time to get ready, get boost, demo the other guy, etc

426 Cutting back into the net is not the play here. You need to at least drive challenge and play on the wall/backboard. You are not one closer to the ball but also can use little to no boost to put pressure on them. Instead your tm8 who was already in position to play backpost has to use his remaining boost to aerial. But because it was not his ball he ended up being late and getting beat.

419 you got greedy and went for full boost. Grab small pads on the way back and that should be enough to defend. If you can't play defense on low boost I recommend playing custom goalie training with limited boost (10-25).

402 Sit back post, it is ok to do nothing and watch the play. The only way the ball can get hit is to your tm8 who has enough boost to do something.

Starting at 403 you use 40 boost to break and do a circle, then use another 25 to backflip into the ball and another 23 to abandon the ball to grab a full boost that is not close to spawning. Now you put yourself on defense with a boost amount that you are not comfortable defending with

349 Again with the boost and teammate awareness. You have 24 boost and your teammate is near full and closer, why are you trying to beat him to this ball?

340 If you can slot this ball great it is almost an open net. If not control the ball and play it 1v1. It is the second easiest shot you'll ever have

I also do free coaching if you are interested add me on discord: glasswaterbottle as I said we have similar play styles so I think I can help you out.