Check the basics - all plugs wires on correct cylinders. Were you checking the timing during breakin? I do this everytime since I did my first build because you will know immediately what is going on with the timing. For example, how far is it advancing, is the timing consistent at a consistent rpm, and is the light coming on at every revolution?
If your timing is correct (or close) I would guess you have a severe lean or severe rich condition based on a touch of the throttle stalled the engine. This is assuming that carb is operating properly. Did you smell gas in the exhaust when it was running, like a severe rich conditon, the smell would be obvious.
Personally, I would restart it with the timing light and see what's happenning, also be ready to check your float heights with it running (how did you set them before starting). I wouldn't be to worried about the cam if you lubed it properly.
I've been right where you are the 1st time I built a motor. I didn't use the timing light and it took me a day and half to discover that my Cloyes timing set was marked incorrectly on the cam gear. Alot of disappointment was felt until I figured it out. Since then, using a timing light while someone else cranks it over allows me to verify that everything is fine immediately when the cranking starts, or I know before it ever starts that the timing is out of whack and I need to find the cause.
Just my opinion for what it's worth and bear in mind I don't claim to be an expert.
Keep your head up and recheck the basics and then give it another whack.