Odds are that some one noticed, a bra will show through a sweat shirt easily. If you bend over the sweater will be pull tight across your back revealing the outline of the bra.
I find people don't see something they're not expecting to see. Maybe someone has noticed... but no-one has said anything.
The crossdressing community is one that needs to stick together and continue to be there for each other for whatever one needs. We are always trying to improve the forum to better serve the crossdresser in all of us.