Rules-- shifting a scrabble tile

If the turn isn't over (i.e. the points haven't been tallied), then I don't see why or how it could be a violation.

For example, let's say I want to add XAMPLE to an E, to make the word EXAMPLE. I put my tiles down. But I've miscounted, and there's only room for XAMPL. That's obviously not a word. Shouldn't I be able to take back the PL (although I've just given away what 2 of my tiles are, an error that will likely come back to bite me unless I swap tiles)?