I like her but i need help?

i like this girl in my english cl but i don't know what to do. I'm shy (we're 18). i wanna talk to her but i don't know what to say. we've talked like 2 or 3 times but it was by luck.Then Monday( her group and mine did our presentations. I was all ready to tell her at the end of the cl that i like her presentation but i decided not to. Then thursday i was gonna say hi and work up the courage to tell her her presentation was good and i liked the guacamole that her group made (bla bla bla) but she wasn't there. nothing seems to go right(something else happened on valentines that didn't go right) i don't wanna give up cause i really like this girl. does anyone have an idea on what i can do cause when i finally get enough courage to do something it doesn't work out. she sits in front of me and we have cl together only on mondays and thursdays.