From what I understand from previous posts here, you can change any part of your AACOMAS after submission, where in other applications like AMCAS/TMDSAS you can only change your contact info/demographics.
So go ahead and try adding shadowing experience to your work/activities, and resubmitting your AACOMAS. Although, if it was already listed under your work experience... I don't see why you would add it again. Just put shadowing in the description box if it's already in your work experience.
When you resubmit, it won't start over from scratch. You'll have to check all those boxes again, and submit... but you don't have to pay anything. So I assume that you'll still only have 2 weeks of waiting left.
Hope this helps.