OIC...you're a rug-rat installing for a store or a shop and they have been withholding a sum from each job. I don't think that is a legal retainage in that case. In fact that isn't "retainage" in the normal legal-sense of retainage. That is what is known as a "set-off". In some states that type of withholding is not legal, don't know about Maryland.
So I'll bet they also didn't withhold taxes and they called you a subcontractor and would send you a 10-99 each year when in fact they controlled your every move while you worked for them and in reality you were an employee. This assumes you filed a return and paid taxes annually.