Yes, that's right. The AOR is the acknowledgement of receipt, and it is the first official document that you will receive from IRCC. It will include your application number, which you will need to use to track the progress of your application.
The UCIXXX number is your Unique Client Identifier, and it is used to track your application in the IRCC system. It is not always updated immediately, so you may need to wait a few days before it appears in your GCKey account.
I understand that you may be concerned about having done an upfront medical exam when you were exempt from doing one. However, I do not think that this will be a problem. IRCC will be able to see that you were exempt from the medical exam, and they will not penalize you for having done one.
I would recommend that you wait a few days and then contact IRCC to let them know that you have done an upfront medical exam when you were exempt from doing one. They will be able to advise you on how to proceed.
I hope this information is helpful.