Congratulations on your bub!
My breasts are the opposite - my leftie has the greater capacity.
Personally, I would just be feeding from both sides as if there wasn't a difference between them KWIM? You are only 3 weeks in, so your breasts are probably still producing more than you need. It can take a few weeks for them to regulate to how much bubs needs. As the others have said, I would definitely not let your right breast get too full and sore.
You are doing a fabulous job and hopefully Barb can help you out further.