I put lawn mower gas into my leaf blower. Now I can not get it to start. The motor run over but will not start.

You might have burned out the rings before the engine could seize up... (the only oil they get is mixed into the gas). I bet the compression is now too low for it to fire.

Hi,
I agree. Likely the sides of the piston have transferred metal to the ring grooves trapping them and not allowing them to move against the cylinder walls to give enough compression. Often if you have the skills, the engine can be partially torn down(remove cylinder), break out the old rings and use a piece of the broken ring to clean the ring grooves. Then new rings and a new base gasket will give you a second chance. Third chances rarely happen, though.
Peace,
Clarke