I'm upset that my partner did my half of the project
They pulled their weight! What made you feel upset about that?
He tried to cover it up by doing a few extra hours's work without my knowledge.
It's understandable that you feel upset. Your partner should not have made this decision without consulting you, and he should not try to take full credit for the project, since you were willing and able to contribute on your own.
I'm going to talk to a manager about it.
I'm starting to understand your frustration now, I agree he shouldn't have overstepped his boundaries. You are a team and things should be done together. I hope the manager can be a good mediator between you two, and things would get back to normal!