Bra Fitting!!

I'm going with my friends to get a bra fitted (cause I'm too shy to go alone) I'm just wondering what time expect. I'm not exactly out yet despite being on HRT for 15 months, but I'm getting nervous. How invasive is it? What are some signs to look out for that they're doing a good or a poor job? Ive heard Victorias Secret is bad, is this true? How long does it take? My anxiety is through the roof