What can I do?? Is this just an excuse?

So, my girlfriend and I have a great relationship, and she is currently in japan as an exchange student. We are on summer break, she will be a senior, I will be a junior (in high school). We go to different schools and live about 40 minutes apart. She has recently been saying she doesn't know if our relationship can go on once school starts because she will be busy with all AP classes and will soon be getting a job. I convinced her that we can at least try but she isn't a confident person. I told her I will be patient and not demanding and can handle it. In all honesty, of all the girls I have dated, she is the ONLY one I believe I have a chance at a future with. Just thinking about when that time comes makes me sick and feverish.. Any and all advice is appreciated..