Pretty Sure? Is that a YES or a NO? If you werent absolutely 100% sure it was downgraded you should have reported it. What you really should have done is researched BEFORE you submitted AMCAS, which you may have been able to do by logging into your DMV with your license number.
Having said all that, I wouldnt worry. If you get accepted and if this comes up, the worst that will be is a request for a letter to dean explaining (they just want the paperwork for their files). A VERY VERY BRIEF paragraph of just a few sentences will be enough. Leave it alone until then