Good on you for catching the fraud immediately.
Immediately alert your bank to the suspected fraud. I would even walk into a branch, as then, they will instantly grok that you're for real and not working a scam yourself. Tell them you doubt the veracity of the check, cancel the deposit and ask them to waive fees. (it doesn't actually work that way, you can't "stop payment" on a deposit, but it tells the bank where you're at on this, and asking for the fee waiver may well work!)
This is almost certainly a fake check overpayment scam - they've been doing these scams for decades. They send you a check for more money than the item or service you are selling, and ask you to send back the overpayment. They pressure to send the money back FAST, and in a form which is non-reversible like Western Union, gift cards or Bitcoin. They deliberately code their cheque with defective routing data so it takes longer than usual to bounce.
Now your bank has no idea how long a check takes to bounce/clear. So the bank gives a fixed amount of time that is based on a TYPICAL clearing time and then releases the funds into your account. You didn't know that, did you? You thought when it releases into your account, it has positively cleared... so you send the money on to them. THEN the check bounces.
They know every vulnerability in our systems. These scammers are really good at it. We think of them as morons because of all the obvious errors we see in scam emails... but even those are smartly chosen and deliberate. Don't ever underestimate a scammer.