Wow, I am really shocked at all the responses telling the OP to tell the truth, come clean, even knowing that his girlfriend will dump him for the dishonesty.
I'm gonna be the only one here to spit some truth: When you've dug a hole too deep to climb out of, sometimes you have to keep on digging until you come out on the other side. OP, you're best bet is to keep the lie going. Tell her you got into an SMP at the med school you decide to attend. If you are lucky, she'll have to live somewhere else next year for whatever her plans are. Best case scenario: the long distance proves too much for your relationship and you split ways and never have to deal with this. Worst case scenario: she falls to pieces, makes no plans for the future, and comes to live with you at your school of matriculation. Things aren't over at this point. You live the double life which should be easy as a SMP is probably as busy as a first year med student. If your gf then gets accepted into the med school you're at and you finally have to confront this head on, you tell her that you did so awesome in the SMP that they made a special exception and allowed to you to move straight to the second year class. This may sound extraordinary to her at first, so just remember this: It's not a lie, if you believe it.