$BTC are effectively holding 10,000u. Based on an average fee of 0.04%, the opening fee would be 4u and the closing fee would be 4u. So, without doing anything, you would incur a total contract fee of 8u. Don't underestimate this small amount; over the course of a day, if you open several orders or frequently trade short-term, this becomes a significant cost. If there is a rebate, you can get back half of these fees, which adds up if you often trade contracts.

Additionally, everyone must ensure to trade on reputable exchanges for peace of mind regarding your assets. Avoid unknown exchanges at all costs.