congrats it sounds like a great opportunity. Dont worry too much, obviously they saw something in you they liked when you were just being yourself. Be as honest as possible. Explain to them your school situation. You are majoring in that field so I dont see why it would matter how far long you are in your degree. Unless you told them you were further along than you actually are.

You can google resume samples and use a template. Be honest with the work experience you have. Trust me as someone who has looked through hundreds of resumes and interviewed possible employees all experience is relevant. Anyway whatever happens it is a good contact to have.