I took a 401(k) hardship withdrawal for closing cost for my residence. I took $10,000 because that’s what the estimate was for closing, closing cost went down. It only cost me 6000 to close. I now have 4000 extra dollars which I had 30% taken out of the word draw. My question is do I have to return the other $4000?

A withdrawal in 2019, not a Loan, from a 401(k) will be reported to you on a Form 1099-R by the plan administrator.  You will receive the 1099-R in January 2020.  The taxable amount of the withdrawal is entered on your federal tax return and taxed at your current tax rate.  Any federal taxes withheld will be entered on your federal tax return as a tax payment.  If you are under the age of 59 1/2 you will be assessed a 10% early withdrawal penalty on the withdrawal.

A withdrawal versus a Loan is not paid back to the 401(k) account.

Not only do you not have to return any of the money to the account, you are not permitted to return any of the money to the account because hardship distributions are not permitted to be rolled over.  You are stuck with reporting the entire distribution on your tax return.  The amount withheld for taxes will be credited on your tax return toward your overall tax liability determined on your tax return.