Women-I'm chicken shytting out with some attractive girl at school, can you help?

This girl has shown me that she likes me even. She is very attractive. Way above average looking. Cute all over. She has been attentive to me, and has even greeted me when I have come to school, unlike how she greets other people. She has done what I think could have been flirting. But even knowing that this could be true, and most likely that she likes me, I can't seem to get past my little boy-like shyness to really speak with her; not yet anyway. She makes me feel quiet, and mousy, when she speaks to me. I keep telling myself, I'm not shy; I can do it, and I'm going to do it. Is it too late also? This is the 3rd week that I have done nothing.