How can I win her back? :(?

This girl and I have been dating for 2months. She's 20, I'm 23. She sporatically joined the army reserve and told me she's leaving in 2months for 5months. 2 weeks ago, we got into an irrelevent argument and toward the end of the night, I said out of impulsiveness and frustration "I don't know if this is going to work out." I regret it. The day after I said that, I called her and we talked about it. I appologized, wrote her a letter that included a poetic song, and we agreed to keep seeing each other. However, since I said "I don't know if this is going to work out." it has damaged the relationship. She acts so distant, like she's already moved on. We had a talk yesterday and she told me she didn't think it was going to work out because of timing and our different schedules. At the end of the day, I told her to give herself time to think and ask herself "Is this what I want? Will this make me happy?" I told her that she'd be missing out on something special if she were to cut it off now. I haven't heard back from her since those texts. And knowing her it has to be one of the two things: she doesn't want to talk anymore OR and she's thinking about it and doesn't know what to do. :( I've tried so many things already, pretty much everything I could do already. I sent her a little thoughtful christmas present and I don't want to bombard her by texting her billions of times throughout the day.. How can I win her back?