At this point probably not, I withdrew early last month which could have made a difference.
But also think about the poor secretaries who have to deal with dozens of withdraws right around May 15th - I bet they would appreciate a few coming in early so they get to go home before 8pm on the 15th. Just call the school you've chosen and make sure there is nothing else due by the 15th, once thats all set send the withdrawal letters.
Also, by withdrawing 2 wks early there is no concern of a letter not making it to them or not getting processed in time and the school you did choose getting pissy with you thinking you're still holding more than one acceptance on the 15th.