Did I screw something up?

[Creektrails]

I removed the side cover that holds the oil to put on a new gasket due to a oil leak. The starter gear came out when I pulled the cover and I put it back fixed the gasket and put everything together. Now the starter won't turn the motor over. I pulled the starter back and it spins when I turn the key but when I put it back in the motor, nothing but a click.
Could I have done something when I had the cover off to make it seize? I didn't touch anything while the cover was off except for the starter gear.
Would prefer not having to take it all apart again.
\Thanks