GD is right. At least you realized your mistake and wants to make amends to your girlfriend, dArK_wOrLd_LiNk. Were you wrong? Sorry to say, yes.
Because you shouldn't have gotten mad because your girlfriend couldn't go out with you. She might has her own reasons and asking with the word: "why" will avoid this in the future. ^^
But don't take it too hard. We make a mistake here and there in our lives, and this is just one of those stages in life that you need to gain experience on. Take this as a test, an experience, to make yourself better and to make your relationship better in the future.
To say that you don't fight with your girlfriend is a lie. EVERYONE fights, no matter who.