He doesn't have much confidence that he is going to be able to fly up even a little bit, but with Aziraphale helping his motion it did make him understand a little more about how it was supposed to feel as he did it.

With considerable effort he tries to repeat that motion and does it slightly faster so that eventually his feet do seem to lift off the ground. It shocks him so much that it immediately sends his rhythm off and he comes back down, stumbling once more into the other man.

"Did I..was I.." failing at flying? Yes..but at least he got off the ground!