What do I do about my girlfriend?

When we started out we were perfect. She thought I was amazing because she had never been with a guy like me because her previous boy friends could care less about her and just didn't really try and treat her the way a girl should be treated.. Well now that we've been together 6 months, she's getting a little bit cocky (not really the right word) anyway she's so used to me doing things for her and saying yes to everything that she gets mad when I don't impress her and when I say no to something. Almost as a spoiled child acts toward his/her parents. It's really getting to me and I need to know how to tell her take it down a notch. This is my exact night... Pick her up from a hockey game at 10:30, come back to my house, she asks for another damn back massage like every night and I say no, she gets mad so I give in, she falls asleep, I lay there until 11:55 because she has to be home at 12 (yes we are young.. 17) we pull up at her house, she gets out and says if you want to say bye then come to the door so I do. Then she walks to the top of her steps when I get there and she says you can come up here. At this point I can just tell that she doesn't care if I kiss her goodnight.. I've been sweet to her, she liked it, now she's taking advantage of it. Every night I do things for her and get no appreciation I'm return. Nothing! It didn't used to be like this and no she's not mad at me