I'm really presuming a lot by telling you this, but...
I'm thinking "hey, you got through the hiring process; you may have qualifications which aren't apparent to you yet but which will surface when the time comes."
Also, not to insult your intelligence but it is so normal to feel that way with a new challenge.
OR - could be you're right and you took on too much.
Will be interesting to see how this pans out for you. Good luck, Loco.
ToHelp