I know very little about the YC application process, but if you are confident that the problem you are tackling is real, and have done your homework, I don't see why you would need to present a phony picture of yourself. In fact I'm pretty sure that the YC folks have enough smarts and experience to pick out phonies.

If you're presenting the phony picture because you don't really have a clear understanding of the problem, then yeah, you will have bigger issues with your business outside of getting into YC.

If you've put in the work and still feel like a phony, try to ignore the feeling - it's probably just the impostor effect.