What if we met tomorrow? vs What if we meet tomorrow?

I just asked a friend: "What if we met tomorrow?" My girlfriend called me out on it and says it should be: "What if we meet tomorrow?" In my head both sound fine, but I know I couldn't say: "Could we met tomorrow?", so I'm starting to doubt myself. It does seem strange to use the past tense "met" to describe a future event, so is it technically wrong?

Thanks in advance :)

A sentence beginning with "What if" introduces a sense of hypothesis, assumption, or condition, which doesn't reflect the current reality.

This construction follows the rule of conditional clause, in which the verb is in the simple past.

Other examples:

What if it rained? Would you still go ahead with your plan?
What if you won a lottery? Would you still keep your job?

In your situation, you could also ask: "How about meeting tomorrow?" or "Could we meet tomorrow?"

NOTE: The answer addresses OP's concern that what he said could be incorrect, which is not. "What if we meet..." isn't wrong either. It may be a suggestion or invitation.

Both "What if we met tomorrow" and "What if we meet tomorrow" are idiomatic English. The former is hypothetical (and contains the idea of "What would happen if we met tomorrow?"). The latter is closer to a suggestion.