The valve is sized to fit the root and to work within the aorta, which differs for each of us. A 21 is within the normal range.
You were not born an athelete, you became one. Your heart adapted to the workload, but didn't grow a bigger valve for it.
If the valve installed is too large, it will begin to leak (regurgitate or have insufficiency), because it won't have enough room to open and close freely. It will deform as it functions, continue to stress your heart with leakage, and its life span will decrease. We have had people get valves too large, and they have to go back early for resurgery and deal with the leakage until they do.
The things to look for are good remodelling of the heart in the first six months, good aortic pressures in the echoes, and proper movement of the valve cusps. If those fall within the normal range, you have received the right size valve for you.
It ain't the meat: it's the motion.
Best wishes,