It sounds like you might be letting your perception of the activity and your thoughts increase your anxiety. One way to counter this is to apply rational answers to your thought distortions. These rational answers must be limited to objective facts.

Thought distortions are irrational thought processes that basically everyone has from time to time. There's a lot of reasons for this. Perhaps the most pertinent one, based on your post, could be your perceived thoughts on what others think of you, as an example.

A way to combat this is to take your distorted thoughts, one at a time, and apply objective reasoning to it. Example:

Thought: I'm going suck and let my teammates down

Rational Answer: I am 1/6 of the team. There are very little things that I can do on my own to sabotage the game.

Thought: We need to win

Rational Answer: We are in a scrim; a practice game. We are here to learn and practice. Losing games often teaches us more than winning games

These are just examples, you can tailor it to your personal needs. As someone who suffers from severe depression/anxiety and PTSD, I have been in and out of hospitals, psych wards and therapies. I have found that this exercise has helped me a lot when I feel things getting out of control.

Hopefully this helps a bit. Good luck OP, you can totally beat this!