I, a trader from GLOBAL GOLD&CURRENCY CO., have established a 16 lot short position in the EUR/USD exchange rate, but the slippage has been severe, resulting in significant losses for me

I opened a 16 lot short position in the EURUSD. This was made up of two 5 lot positions and one 6 lot position. I calculated my sizing so that my 20% automatic stop out would only be triggered if the market breached 1.0904. However, as shown in my screenshots, the market closed my 6 lot short position out at 1.08922. At this level in the EURUSD, my margin level would only be 75%, well above the 20% automatic stop out level. This is quite concerning as I am not being offered the leverage I thought I had, namely 500:1 with automatic stop out at 20%.