umm
It depends, a lot of girls in high school, or maybe just in my high school, are inexperienced. Your best bet would to just get hot n heavy w/her, go 2 steps forward and take 1 step back, but I know many guys that once they start dating a chick and a situation happens, they either pull out a condom or say "do you want to..."
If she says no....it's not necessarily no..if she says it in that 'i dont wanna be a slut way'
Remember that most hs girls are inexperienced, but very curious. Many of u guys think that asking to go further is a no no, but with a young nieve girl it works.