At first I thought it was a big large in the cup (I'm a 40DD and ordered the same), so I was still a bit mobile, and working out in it was just straight up no way.
BUT instead of sending it back I just put it on over another bra (that fit a bit tighter), and behold! the perfect workout combo.
I didn't go anywhere for entire workout and there were significant jumping jacks involved.
SO order smaller than normal, but if you don't try to 2 bra approach.