Expecting 2.5% gains, end up having 10% loss.

Hi guys, I'm quiet new to this world. So far I've been converting one crypto to another to find my gains (mostly busd to btc/doge).. And so far I managed to do some decent transactions.

In the last few days I tried to move over the placing orders game. Just because it seems easier as I can select in advance when to buy and when to sell so I don't need to look constantly at my phone.

So I've done two tests.

On the first attempt I was trying to check at the fee. So the market was at 38500 and I limit buy at 39200. I also place a sell limit order at 39200.

I was expecting only losses due to the fee since I'm buying and selling at the same rate. I ends up gaining 1%. Amazing.

For the second attempt I loaded a proper order. Market was around 40200. I place a buy limit order as 40000 (busd to btc 100%) and a sell stop limit order at 41000/41000 (btc to busd 100%) in this case the selling point is stop limit so if I change my mind I can delete it and place a new one higher or lower. By the end of the day both orders has been filled.

This time around I was expecting something like 2.5% gains but I actually lost 10% of what I've placed ????.

Do you have any clue why this happens?

I also have one more question. Basically the market right now is quiet calm. Movement are too short and maximum gain seems to be 2-5%. I've read that with futures features you can multiply it (up to 20x)... How does actually work. In this futures there are also new options to be filled (it doesn't seems easy as standard offering with limit and stop limit oreder).

Thanks in advance for your help!