The first thing I'd say is don't worry too much that you felt you were informal - I think the interviewing style lends itself to that if I'm honest, as it very much felt like just a chat about myself. I spent the few weeks after my interview cringing at the "joke" I made, and everyday I'd remember a new answer to criticise myself for.
The point is - it's not worth it. You don't *really* know how well you did, although I had an inclination I did well like you said you do, and you certainly don't know what they were thinking. Relax, maybe find some work to do because I know for sure that I was behind after prepping for the interview for 2 weeks, stop relentlessly checking your emails and just let it happen.
