My bike is messed up. It is the type of bike where you can not pedal backwards, like the old bikes that would brake when you pedal backwards not forwards.. However, it has 3 gears. I was riding it and accidentally pedaled backwards very hard and it came to an abrupt stop.. Now when I try to pedal the back tire is rubbing up against the frame of the bike.. What did I do? Did I knock it off alignment somehow?
It sounds like the rear wheel shifted in the frame. Look closely at the axle where it connects to the frame at the dropouts, you may be able to see that it shifted.
If you have the tools, loosen the nuts holding the rear wheel in place and you'll be able to recenter the wheel in the frame. As you recenter the wheel also pull back on it to keep tension on the chain. You want the chain to be taut, but not so tight that it binds as you pedal – the drive train won't be perfect and there will be spots that are slightly tighter than others, if they chain is too tight they will bind. Finally, tighten the nuts up again and you should be good to go.