ok what you need to do is to actually go up to her and talk to her, and avoid looking down at your toes or erring and umming. Those things just show that you are not confident and they will be turned off. It also shows that you don't talk to girls often since you are nervous when you are talking to one, that's also a turn off. Approach her like you would approach your mate, and be cheerful and casual. Talk to her about stuff you both do, or something both of you just did (like that test for example). But always remember be casual and act as if you are talking to one of your mates instead of a stranger. Confidence is the key! I wish you luck.