boot into CWM recovery
do a backup (not necessary, but recommended)
flash the rom .zip file
Shouldn't mess anything up as far as your data and rom setup is concerned (but there is always a possibility which is why you shuold do the nandroid), but might fix any errors that happened during the initial install.
If this doesn't work, I would probably SBF, but someone else might have some different input if you aren't in a hurry.