I accidentally took 2 Allegra (fexofenadine) 180mg?

No major problem. If this is a plain antihistamine with no decongestant in it,I would expect no serious problem although some minor drowsiness may occur. As,long as you're experiencing no discomfort simply let the medication dissipate. If you have any further concerns, call your physician.
Ok. You should be fine and taking 2 should not adversely effect you greatly. Increase your fluid intake and try a glass of milk with bread too. Try and remember to be compliant and know when you took the medication, so overdosing does not occur. best wishes.