You traded a very volatile futures contract. When creating a stop loss, Watch the type of order you make. Stop Limit order vs stop loss order
Stop limit order - creates a limit order and the position gets closed at exactly the price you set
Stop loss order - order gets executed at market price. If you market moves do fast. You will find your order getting executed away from the actual price you had set

Which trypeof stop order did you use?

https://www.investopedia.com/ask/answers/021015/what-difference-between-stop-order-and-stop-limit-order.asp