turn show match on record setting off before scrim starts, then it literally doesnt matter how you do in the scrim as it wont show up anywhere afterwards. listen to music between rounds or after you die, and try and keep the vibes up with your team.
Your expectations are fucking you up :) You'll become more confident as you play scrims, losing is not a bad thing since scrims are literally just meant to help you get better, not like it's the VLR cup or anything
You are respecting your opponents too much. Sometimes you just need to do something they don't expect like run at them. If you doesn't work then maybe you really are just a worse aimer than your opponents.
From the time I played comp overwatch I found the easiest solution was just to follow a nice simple warm up. Nothing to serious and just to play more become more used to the environment and get your brain back to that flow state it is when your normally playing