I play EC in sessions, and I'd be cautious about doubting your audibility and get a second opinion.
The sound from a concertina goes out sideways and other people may be able to hear you very well, even though you can't hear much yourself.
I like (if possible) to sit in a corner, with a couple of har d surfaces on either side of you the difference in sound can be quite surprising and the "feedback" is very helpful.
Chris
ps DH, who plays fiddle has the opposite problem, he can hear himself easily enough, but a fiddle a few inches from the ear may make it difficult to hear other people!