Yes, you need an fcm or ib. Easy enough to get (several forum sponsors)
This thread is almost 2yrs old...but pretty sure this all was already addressed. And no, it wasn't not knowing the difference between a stop market and stop limit...
Stop orders are divided into either stop MARKET or stop LIMIT orders. So, in your case, had the market gapped down and was trading below your "stop market" order, then your order would have been executed immediately as a market order. If your order was a "stop limit" order, then your order would have become a limit order. Hence, I assume you chose stop limit rather than stop market.
This thread is almost 2yrs old...but pretty sure this all was already addressed. And no, it wasn't not knowing the difference between a stop market and stop limit...