"Sometimes it feels as though I can't sit still in my skin"...
That is perfectly normal, it's a nervous reaction in your situation. Whether it be before competition or right before you attempt an unbroken barrier - you have to deal with nerves. Even defending your life.
Control how you feel, or focus on channeling it where you need to go. It's fine to feel jittery before you attempt a clean and snatch at 285lbs, as well as when you are about to go face to face with last year's State Champion in any respective sport.
Being able to handle your nerves and channel your energy towards what you want isn't easy at all, but it begins with focus. And that's why we believe in it so much. If you focus on the fact that it's fine to be hyped for competition and intense settings; you begin to take control. Once you have control of that feeling of your nerves, use them at your advantage.
If you can't seem to control your nerves, control your breathing. There are many methods of calm-down breathing that you can employ - just focus on relaxed full breaths with a pause in between. Easy and effective in gaining control of nerves quickly.
Lastly, if you are nervous for failure... just try your best. Failure is on the pathway to success, so you can't always win but a winner always tries.