Let's talk about one-way and hedge mode.
In one-way mode, you can only hold a position in one direction for each trading pair at a time: if you're holding a long position and place a sell order, it will first reduce your long position.
To be honest, I hadn't noticed this before: if you're not familiar with hedge mode, one-way mode is less likely to lead to mistakes.
By the way: $BTC is currently at 83550.75, down 0.077% over the past 24 hours.
Before opening a position, check the liquidation price. If it's too close to the current price, reduce your position size.