Marriage is a promise of forever, so there is no need to rush it. I can understand your desperation of staying close and committed since you now live so far away, but marriage is not the best or only way to do it. If your love is strong it will find ways to overcome the distance.
A lot of people get what is called a 'promise ring' which is a ring that promises one day you will get engaged. It's for those not quite ready for marriage yet but feel that they will be one day with each other, and it's a promise to hold onto that love. You could of course make the promise without a ring.
Is she planning on going to the same college as you when she graduates? If so, things will be easier on the relationship in a year or so when she moves to the same place as you. If not, you will just have to continue to find ways to keep your love strong in spite of distance. Communication is a huge key.
Talk very often. Tell her all the things, the little details that are going on in your life, and ask her the little details of hers. It will help you to stay close.
If the distance is putting way too much of a strain on the relationship, and she isn't going to move to Arizona, you'll have to decide whether or not you should move to be closer to her and switch schools.
There are two ways to look at that though, and you are the only one who can judge that. One is that if your relationship can't handle the distance you may have to end things, if this school and being in Arizona are important to you and your future plans, then it just wasn't meant to be.
The other way to look at it is that you don't want to end the relationship so will move back to NJ if it has to come to that. Consider, however, that if you do move back to NJ and things still don't work out between you two, whether you will have lost a lot by leaving Arizona.
You'll have to decide which loss you're more ready to handle.
I wish you the best of luck, and hope that I was able to help in some way.