You set the stop loss when the price reaches that point to start activating the order. But because the price moves up too quickly, it matches the order at a higher price than the stop loss

I'm new to this, so I don't quite understand! Those who have been playing for a long time could explain a little to help me, right?
Why did I set the SL at: 1.243 (which resulted in a deduction of 280 U)
But it swept the tail like that, running through the SL up to 1.2886 (which resulted in a deduction of 627 U)
I'm asking to set it up for next time! Thank you.