Dude i have used these exact words (minus the 'go on, come back' part) on two seperate occasions and it worked!

They stood there looking like a deer in the headlights, totally blown away by what i had said. After waiting a few seconds they bit their bottom lip and nodded their heads and off we went

Iv also used it on about 4 other girls and pretty much got the same reaction that you did. You just gotta accept that some girls will be down to fuck and some wont, not matter how good the signs might appear.

Main thing is your being a man, stating your desires and not being ashamed about it.

Oh yeh, i once asked a girl
'So do you like doing crazy exciting things'
'Yeh why?'
'Iv got an idea which means that me and you will have a crazy exciting time together'

I took this girl back to a local hotel and shagged her til they threw us out