Daft question but are you using a knee pad? Also as Rob said it sounds like "nerves" and we all get it but it's about how you deal with it. I find that I have to take a Me V Target approach to my shooting and block out everything else like how well my partner is doing etc.
When I was 5 I wanted to be like George Best
At 10 I wanted to be Nigel Mansell
At 40 I wanted to be like Tiger Woods
At 50 I want to be like Gilly
Just shows how life can kick you in the nads