I have around 300 hours and it still happens to me nearly every time I fly. Often I'm so scared that I find myself wondering why I'm putting myself through all this. But like you, as soon as I get in the cockpit and start the checks, I'm just fine. An instructor friend assures me it's quite normal, and that she always used to feel like that too. She says she doesn't now - but she does have over 2000 hours. Nice to know that feeling stops eventually though isn't it?