My main girl at the moment rejected my first kiss attempt, and said repeatedly she was NOT going to sleep with me about 4/5 times through every stage of kissing, clothes coming off, me licking her, her sucking me, all the way until we actually did fuck the first time. I just ignored it, backed off a bit, and then carried on.
Unless she says it in a really angry way, it probably means "not yet" "maybe later" or "game me more," usually to help her feel like less of a slut and/or to see how much you're willing to try i.e. how much you really like her.
The ONLY way to fuck things up is to act defensive, angry or hurt, and especially if you say things like "but I thought you liked me

" and gay shit like that. She will likely see it as a compliment, even if unwanted, and you are free to try again multiple times, especially if her 'rejection' involves even the slightest blush, smile, giggle, or IOI of any kind.