You can most certainly practice magic and still be Christian. Prayer is a form of magic/spell casting, it just isn't called that by most. Your beliefs are your truth. I have a friend who considers herself on monotheistic pagan. She works with one she calls the Source, from what she has said "He" has many similarities to the Christian God. To her the Source is one who created this Realm and all the life in the Light in it. Her Source is technically neither male nor female, but she calls Him male for ease of speaking. She does believe that the other Gods and Goddess of various pantheon do exist, but she chooses not to work with them.
Magic, and spells specifically, is essentially focused thoughts/intent that you pour energy into and then release that energy. You don't need to call on any deity or spirit for that, although many do. Belief is a huge part of whether something work or not. If you don't believe it will work then it won't. If you don't believe that something exists, then it doesn't for you. That doesn't mean that it doesn't exist at all, just that it doesn't in your reality/truth. If you believe you can't see the astral, then you can't. You can choose to change those beliefs on your own, but no one has the right to force you to change them or to push their beliefs onto you. Magic is unique to each and every one of us. No two beings practice magic in exactly the same way. What works for one may not work for another. Just follow what feels right to you and you will find your path.