Was this a new mower? I only ask because two cycle lawnmowers aren't as common as they used to be.
The bad news is, a stuck engine is usually terminal. You can try removing the spark plug, pouring a couple tablespoons of motor oil,(automatic trans fluid works best),into the engine, LEAVE THE PLUG WIRE DISCONNECTED!!, and reach under and turn the blade to try and free up the engine. Be sure and clamp the operator presence bail against the handle first.
You might break it loose, but the damage, in the form of scored cylinder walls/and or rod journals, is done.

If it does come free, mix some gas/oil, heavy on the oil, and try your luck. It might mow for years, or it might mow for minutes.

It all depends!! Been waiting for my chance to say that...

"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.