Bummer.... That's right. I did that once - wasn't too bad to fix, depends what method you'll use to deepen that ledge. Or maybe you won't have to tighten the head. Another possibility is an 8" macrame ring (yes, really - and you can find them super cheap online) between the head and the rim. It will buy you a LITTLE more room for tightening the head, and it would also brighten the tone (if you are seeking that) - a low budget but effective "tone ring" of sorts.
Also, does your fingerboard extend out over the head? If so it will be very hard to change the head (yes, I did that one, too. Didn't fix that, just had to take off the neck to switch the head). Then againin you may never have to or want to swap the head.... But an 8" fiberskyn Remo (sp?) head would really punch up the sound.... A worthwhile upgrade, IMHO. Depending on how close the fretboard is to the head, the macrame ring mentioned above might not be an option.