I'm also the funny friend, not a story teller, and was worried about the same thing. The key is use those skills to react (through jokes) to things that everyone will understand. Most jokes are people reacting to things. You just have to figure out how to package and present that reaction. A good way to do that is to listen to your favorite comics, think about what they saw, heard etc. and how they took it from that (the actual events) to what they're saying on stage (bit/joke). Writing original comedy is making the audience see the world through the lens of your brain.

Scared of writing? Silliness. Get a notebook and start writing about things you find funny, or even just rant about stuff. It'll probably be all junk in the beginning, but even when you get good, you're still gonna throw out a lot of material. If you start writing and are having trouble or have questions, go ahead and post them here or you could even pm me if you want.