What should I do about this girl?

So, over the summer of '09 I went to Europe with 7 other kids from my school, and I became fairly fond of one of the girls that was there with us. We became decent friends during the 10 days, but then we went back home. I asked her to our Homecoming dance in the fall, but then no real relationship ever really came of it. Since then we have hung out a little bit, but nothing ever just us two. I really like her now and don't know what I should do since I have asked her out and tried before. My friends think that she is into me, because she has asked about coming to some of my baseball games this spring, but I am not sure if I totally believe them. They say there are other similar incidences, but I didnt notice them apparently. I dont know if I should ask her out again or not due to the proximity of the last "attempt" or if she even likes me at all. I am fairly shy so its not easy for me to just come out and ask someone out. Any advice would be great, Thanks.