Some people gain weight because you’re pretty inactive for about 6 weekish, so if you’re used to going to the gym and being really active then you may gain some weight. Also, you’ll be bloated for at least a week from the medication but that’ll go down.
I don’t think you’ll be small with 340s, I think maybe you’ll look a dd and measure bigger. But if you’re worried about being too small, see your surgeon again xx