How do I get my Ex-girlfriend back?

So I was dating this girl named Brianna for alittle over two months. Things were going great, or so I thought. Then one afternoon, she didn't seem like herself. She told me that she was sick. I gave her a kiss goodbye and told her that I hoped that she felt better. When I got home I texted her and asked her what was wrong, because she seemed like she was really brothered by something other then just being sick. She told me to go on aim. So I did. It was there that she said "that the relationship was getting to heavy for her and she couldn't handle it anymore." So yeah, she dumped me. I want to know how to get her back, or at least get her off my mind. I see her everyday because we go to the same school, but also because she is friends with some of my friends. I can't stop thinking about her and how much I miss her. Things aren't really good between us anymore, we aren't fighting but it seems like she wants nothing to do with me. She is usually pretty quiet around me and we don't...