I rejected my cousin, did i do the right thing

I already asked a question a few weeks ago on here and told you that my cousin was flirting with me all the time. This thing started years ago but it intensified when I turned 18, she even playfully asked me to live with her after she broke up with her boyfriend, like '' do you want to live with your parents or with a girl? ''
I actually really liked the attention, she's as attractive as the hottest celebrities out there, when I told my best friend that my cousin ( I showed him a picture of hers ) was flirting with me, he laughed in my face.
Anyways, last Saturday she drove me home after a night out, before I got off her car, she kissed me and put her hand near my D, I reacted like '' what the fuck are you doing? '' ( but I did want to do her ), she said that she's always been into me and that she finds me really attractive, I said I like her too but I don't want to cross the line.
She blamed the alcohol the next day but she was clearly not drunk, I said '' yeah it's ok, I know you would never do something like that to your cousin when sober. You aren't such a pervert. '' LOL.