Just accept that you will, at some point, mess up and feel silly. Everyone does.
The thing, when it happens, you realize you feel silly in the moment and then you move on. Feeling silly isn't really that big a deal. Particularly when you're starting out, because you'll either be performing for people you know (so they're nicer to you - and if they're not, maybe hang out with nicer people?) or you're performing for total strangers you'll probably never see again and they'll forget about you within moments.
It's a good idea to get out there and get that feeling of silliness over and done with so you get more comfortable.