I know everyone says its fine and you most likely will be. HOWEVER, at some of the pre-dental lecture series classes at my school, we have had several members of different adcoms come visit and present. Almost every one of them said that they have thrown out an application over grammar issues or typos because there are so many strong applications and sometimes that is what distinguishes them.
It is true that you should never go back and check after because it is out of your power now, but for this reason, we NEED to make sure that we don't make dumb mistakes and that we do sweat the small stuff.