Peace be upon you all

for those who have experience in Binance, I bought the Ship coin for $30, the price rose by a large difference of about 250 points and I sold it, I noticed that the USDT in my wallet is only $29.45000 instead of $30,

my question to you guys is where is the difference that I gained from the deal, am I wrong in something?

For your information, I bought with a limited order and sold with a limited order as well, but I only modified the deal to close it.

I hope that the honorable brothers will respond to us or give us advice, thank you in advance.

With my regards