This is my last chance :( how can i go through this please help!?

Tuesday is my final exam , and there is this girl that i really like and im sure about it because although we never talked but i know her very well and i remember a time when she was in the corridor and i was at the cl door window and she was looking at me and blushing somehow but i was a complete (any bad word will suit me lol ) and didnt talk to her , i was thinking of talking to her at the end of the exam or maybe telling her that i have feelings for her, in the past i didnt have the courage but now i do have it because i realised that i would never see her:( What should i tell her and how to open a conversation and how would i act , thanks :)