@whatisit2014,
You may or may not be a racist. Based on your single use of a certain word I can understand why someone would jump to that conclusion, but I will take the high road since I do not know you and I don't think I can judge someone based on the single usage of a word. So I have two suggestions for you.
First, leave this girl alone. She has made it plain to you that the two of you are through. Maybe she does not like the kind of person you are, (one who uses racist language) or maybe she just found someone she cares about more than you. Doesn't matter. She has made it clear that she does not want to be with you. So stop bothering her.
Second, it would be great if you learned from this that people are people, no matter the color, nationality, religion or whatever. Using disparaging language to talk about someone else only shows how backward and stupid you really are. And it might well be why this girl decided she had enough of you.