Playing Bridge last night my partner opened 2NT, showing 20-21 points. I had 11 HCP and a five card major. I used Jacoby Transfer, calling 3 hearts and my partner responded 3 spades (all OK so far) I then needed to show our possible small slam hand. I did not want to call 4 spades as she may only have had two spades. Equally I didn't want to call 3NT in case she passed. I therefore called 4NT and a big debate started about whether that was Ace asking.
What should I have responded? All Jacoby Transfer pages I find on the net only specify full responses after 1NT.