I removed two three-way electrical switches; they don’t work now
Notice one of the screws is black? The other two are brass. 

Get a 5-pack of colored electrical tape and mark both of the wires to the brass screws with yellow  tape.  Those are travelers and they go to the same place, in the same cable, and are interchangeable (no need to tell them from each other). 

This makes 3-ways a lot easier to deal with.

Also, hook the wires around the screws, they are far more reliable than backstabs. For one thing you can see if they are engaged properly.