<p>Hmm as Unis don’t immediately start looking at your apps, that is if they are not rolling, contact the concerned Unis ASAP and inform them of your mistake. Also include with your email, your info AND your common app ID.
Mistakes happen and they will edit them as I dont think this is that much of a deal-breaker.
Good luck :D</p>
<p>I would not correct this at all. Schools will overlook this sort of error. Your transcript will speak for itself and will confirm the dates of your attendance. This will not affect your admissions chances.</p>