Probably didn't boil it for quite long enough
A good way to tell if it is ready (i.e. will set) is to have a glass of ice cold water next to the mixture, drop some in and if it doesn't turn the water cloudy and holds together it's done - sounds like yours wasn't quite at that stage - have another go - but the 'ice cream goo' sounds deee-lish!
It needs to go solid enough that you can just roll it into a ball between your fingers. If you boil it for more than that you will have toffee.
did you beat it until it goes grainy like wet sand??
Need to do this too to get the right texture, but leave off the heat for 5 minutes before beating and then stir it until it loses its gloss. Stick it in a tin. Enjoy.