Definitely don't take it to a repair shop yet. As previously suggested, I would first wait a few more charge cycles to see if the system software has to "relearn" the charging times. If that doesn't help, then do a factory reset.
Even if the problem persists, I wouldn't bother with bringing the phone to a service center as long as the battery was still charging up at a normal rate and giving you normal battery life. The difference between 100% and 99% is minimal, and there's no harm in not fully charging the phone -- in fact, battery experts would argue that it's healthier for the battery not to charge to 100% on a regular basis.