Hunt down a copy of "go for it". It deals a lot with this stuff. Just remember a little fear is good, it keeps you from getting sloppy/lazy on a skill. You just need to learn how to keep it in check. In most cases the fear isn't of the skill, it's of not doing the skill. The pressure you put on yourself to not fail is great, but remember that end of the day if you don't throw something, the world won't end, your boyfriend/girlfriend won't break up with you, people won't stop loving you. Tumble because you love it and you want to help your team out, not because you "HAVE TO".