After your third sentence, I thought you were going to say "I really need to get to launch". But instead you blamed YC. So that's two attitudes that undermine you.
It requires a tremendous amount of trial and error, as you learn about the market, and the technology. Get data from reality as soon as you can. This requires a kind of courage... and behind it, a pragmatic ability to see how to get that information with minimal work/time, and then personal productivity and energy to get the work that is needed done quickly.
Sorry to be critical. If it's any consolation, I'm totally unqualified to be critical. And some projects do require longer deveploment (e.g. the R&D startups in this batch), maybe yours is one of them.