I did the same thing with one of the cars I bought. I freaked out first though. I'm trying to remember what I did to fix.
First take out spark plug. Then make sure your choke IS OPEN.
I think I tilted the car with carb air intake filter pointing down and let it sit for awhile. Then slowly try to pull start.
If won't pull leave it for awhile.
I honestly don't fully remember but ,I was ready to call the guy and complain.
I'm fairly certain it just needs time for fuel to drain/evaporate out. I may have loosened gas cap also and just let it sit. I know it feels literally like it's vapor/ locked up solid.
Also I put in New spark plug and it worked. I think the problem was thinking you had choke off when it was on,constant starting with no way to release the extra fuel/cylinder pressure.
I hope this helps,just don't panic like I did.
I found it.
Follow this video. I missed some points. Now I remember,of course?
Here's the vid, I think helped me back then.
------------- Instructions -------------
So.
1- Take spark plug out.
2- Take off air filter.
3- open choke fully.
4- hold/brace throttle fully open
5- pull starter fast several time to blow out out extra gas.
6- Install New spark plug if you have.
Or thoroughly clean and dry out old plug.
Try to start,remember to make sure of choke position.
If done right, you should be brapping in no time.
I really hopes this solves your problem.