Blame it on being a startup or the simple fact that you don’t have a ton of letters behind your name. It can be a challenge for an entrepreneur to truly own the fact that they know their stuff.
The easiest way to overcome such a mindset game (and yes, that is all it is, a mental game at hand) is to put facts on your side. Make a list of everything that makes you an expert. It can be formal things like certifications or training. And it can be informal elements such as that you have always been damn good at reading people or constantly redecorating your room as a kid.
All the elements and instances in your life before this moment led you to this exact moment. And you have to believe that on some level, you are fully prepared for it on a Divine and down-home level.