Prone Player–NCAA vs. NFHS

[DrPete]

I had a play where there was a scramble for the ball resulting in one player laying on the floor on his side (not moving). The player who came up with the ball stumbled over the prone player, and as a result took an extra step before he started dribbling. I called a travel.
At the half, two more senior officials told me that should have been a foul (on the prone player) every time.
What should the right call be? (NFHS)