I'm guessing you're at goose spit? If so, I don't think that's what your instructor had in mind when they said not to walk back. In that situation, with the wind going over the spit and blowing offshore, if the board is caught in the lee of the spit and isn't drifting downwind at all, then body dragging in 2" of muddy water until you're exhausted is a waste of energy and time. Stand up, get your board, and commence riding!
Body dragging upwind is an important skill to master for sure, but it has its limits. Ultimately it is about getting your board back without needing a leash....and so if it is shallow enough not to need body dragging, and you're tired, then walk back. I have been caught in a situation where the current was opposite direction to the wind, and couldn't close the gap. What worked: body drag to shore, walk upwind 50m, and then body drag back out, voila. Kiting again.
As well, in many hours of body dragging (unfortunately), a couple things learned: 1) depower your kite with trim strap, you will lose less distance downwind on the turns; 2) better to twist over and be on your belly, like superman style, rather than on your side like you're doing sidestroke.
Good luck and have fun!
[Caesar: Teabag is a long time kiter around here....I suspect this is someone borrowing his account]