Go, do it, and enjoy. If you've been asked to assist, your prof obviously thinks you're good enough. Have faith in yourself. Lots of us here suffer from 'imposter syndrome' - do a search on the forum and you'll come up with lots of posts. We worry people will think we're frauds and will see through us. The way to beat this is to believe in yourself, and also bluff your way through until you really are confident enough. It's important that you grab opportunities as they are given to your thorughout your candidature, so grab this, learn and have fun!