I am attempting to break in my PT-40 powered with a A.P.S .46

I had it running nicely but when I shut the engine down (I do it by squeezing the fuel line to the carb) it stopped solidly as if it just froze. Now when I flip it (yes, I use a chicken stick) its like the piston and prop shaft is tight and it will sometimes be stiff when trying to flip it and the prop will not turn over properly but will just stop solid.

What did I do and how can it be remedied? The engine has never flown before so it was never in a crash.