you think too far into it, Having a girl in your room isnt like your about to commit adultery or something lol Just lie on your bed (or recliner if you have one) and have her lie on top of you, watch a movie or something, thatll give you a good 2 hours of whispering sweet nothings into her ear.. kissing her neck.. etc
Just cuz theres a girl in your bedroom doesnt mean your going to have sex, If your parents are the uptight type just keep the door open, or maybe do the above in a living room with no one around (Plus you get the added bonus of letting her meet your family if she hasnt already which shows your "not afraid to bring her home to meet mom" as it were)