I would say spend more time developing a solid prototype and use that time to find a co-founder. You can't be perfect and there has to be someone out there to compensate for your own weaknesses. With a good prototype, it should be much easier to attract a co-founder and the added time should allow you to really make it solid and increase your chances of getting into YC.
edit: Keep in mind applying isn't a binding, one-time-only thing. It's not like you can't apply for the next round if you don't get in this one.