I fell off my bike, now the gears are acting weird

Try adjusting the shift cable tension.

Select whatever is your middle gear and then use the adjuster nut at the end of the gear cable by the rear deraillieur to line thechain tensioner up with the selected cog. Should improve things a fair bit.

MAKE SURE DERAILLEUR IS STRAIGHT

Amen,

Also chech the mech is not cross threaded in tha hanger.

yeah, the derailleur hanger could be bent; if the guide wheel is crooked and misaligned, the bike will essentially be between gears all the time.

do you have friction shifting or index shifting?

also late for work again oh noes

yeah if you fell to the right, and its suddenly quite wonky, its probly yr derailler hanger, esp if its an Alumin(i)um frame/removable hanger. to really get it straight, you should use the proper tool, but you can usually get close enought for functionality. also, for Al, once bent they tend to get very soft and susceptible to rebending or breaking IME.

Thanks for the advice y'all