Firsty I am not a dr.
You don;t mention how old you are? It is perfectly normal to have one side of the face differ from the other side.
if you look in the mirror and see only your cheeks different and nothing else it seems like all will settle down as age progesses.
I think your cousins will be so happy to see you after 2 whole years they will not even notice your cheeks
Hope you have a good trip, as long as you have no pain or other concerns things should be fine given time
if you have any medical concerns you should see your dr..