Maybe there's help available locally. But most of us assume that we're on our own. And we're usually right. So I'm going to assume that you're on your own.
Here's the good news; there's a lot of help and wisdom to be found in these threads.
Okay. Your chain won't stay on?
Start by checking to make sure that that motor is staying exactly where you put it. Any movement there and you'll throw your chain. Or worse.
If that checks out, then see to it that your drive sprocket is mounted correctly. Straight and true.
If you have these two things set, then I'll bet you'll have no more trouble.
Good luck.