I'm sorry to hear that you had a nasty experience Sarah. Do you have to record your height when you join? I just think that even though 54kg sounds small/slim, you have to take into consideration the height ratio. My cousin is quite a short person and when she was younger she averaged 48kg. On paper it probably looked scary but in person she looked just right for her height. More recently since she hit her 30s she sits between 52-54kg and while she looks good, you can see she's a bit curvier and I know she's a bit uncomfortable with it. LOL actually she's very pregnant at the moment so she's probably around 60-65kg now (that's a guess
I think what I'm trying to say is, they may be judging you solely on the numbers on a page which is a bit unfair. Don't worry about that - we're here to support you Sarah.