Zoe you're prob not going to be able to. But a lot depends on nipple size as much as breast size. I've had boobage my whole life but before I started HRT, because my nipples were really small they didn't look like boobs. But now with nipple growth (plus they're kinda rounding out at the bottom), I'm worried I'd get arrested if I took my shirt off at the beach. I don't exactly know when it becomes indecent exposure. A thick, black shirt or top will hide them best. If it get's wet, the skin won't show thru, and it'll slim the shape of them, making them appear smaller. This is what I have done in the past.
Also, everything Tessa said.