Well first of all, remember this important thing. Don't worry so much, relax, be calm and be confident, he'll like you being confident and sure of yourself rather than nervous. From experience as well, people don't generally like everything to be all about them, so don't make it out as if everything has to be perfect and if he is slightly upset then the night is a failure. Be calm, it'll make him calm, that's the most important thing to remember, be calm and have fun.
Remember that one ^ but as for something amazing, maybe just take him walking on the beach after if he likes romance, if not take him to his favourite bar or something and just have fun with him. For the prom maybe you could make a poem for him and such, but honestly, don't be too worried about it, relax and just stay calm and know that he does love you and he'd love just being with you.