Best advice is to call your brokerage and ask them the difference between their various types of limit orders. Like Fidelity, you'll probably find the order has to hit the ask, go below or above and then back in order to execute. Or, some other iteration. Call Ameritrade.
I believe no. Ameritrade utilizes the NASD for AMEX trading. If you just put in a limit order it was probably only on the NASD exchange. Ameritrade does have other choices where you can pick the exchange you want to trade on but I am not sure if you can use it on AMEX traded stocks.