I'm assuming you're in your D1 year? I would say keep your sights set on OMS and keep working hard. I don't think you can say for sure what's going to happen this early in the game.
A high CBSE score can make up for grades to an extent but you still need to to keep your grades as high as possible. Three As/Bs isn't close to the end of the world and you definitely are still in the running.