I'm a single founder and I had the same doubts as you before applying. But then I decided to apply anyway. Just filling out the application was really useful in terms of thinking how to present my startup. I also reached out to the YC alumni network for feedback on my application and boy are they helpful! Some of the best founders out there helping you pitch your startup even before you are officially part of the network - couldn't ask for more.

My email's in my profile if you want to have a chat.