Post office problem D: I so messed up, what should I do?

First thing Monday, contact both the office where you dropped it off (the tracking info will provide information about the office of origin, so they will know where it was mailed) and the office of destination. If all that's on there is the destination zip code, it should at least get to that office. Once they have it and they have heard from you, they may be able to send it on for you with the correct information you give them.