You have nothing to worry about. These ladies are here for your pleasure and their financial livlihood.  While they may legitmatly enjoy your company, they will want you to have as good a time as  possible so you will come back again.
The size of your member will not concern a good provider in the least.  When I mentioned my size to my ATF, Chantal, she talked about some former customers who were really small.
She did so not in a derogatory tone of voice,just in a matter of fact way.  Remember, while not a doctor, most size differential is when flacid, not erect.
Just do your research with this site and find someone good and everything will be fine.
Just have fun and leave your insecurities at home.