sounds like you just gotta build some more comfort/ rapport with her. when shes saying that it doesnt feel right, basically you havent put her in the right mood, so this could be a cue to amp up your seduction skills
then again, if she's 18, and still a virgin, she's just gonna feel wierd anyway, so you've got your work cut out for you!
Who you are speaks so loud that I can't hear what you're saying
I know of no more encouraging fact than the unquestionable ability of man to elevate his life by conscious endeavor - Thoreau