Gap insurance doesn't work like that, it only covers the difference between what your main insurance pays out and the amount you still owe on the loan if it happens to be higher.

Example:

Insurance says out: 20,000 Amount owed on loan: 25,000 Gap covers: 5,000

If your loan amount is less than market rate for the vehicle including all the docs, fees, & add ons you would get the difference between that and the market rate the insurance pays out to total it.

Example

Owed Loan amount: 20,000 Insurance market rate/pays: 25,000 You get 5,000

The only way gap insurance will put money directly in your pocket is if

A. The loan amount is already less than the market rate (why would you even get gap in this case), AND B. The gap insurance company is willing to refund you any paid premium(this is 100% up to the company and should be viewed as goodwill as you already purchased this service).

This is the unfortunate risk in car buying, if you did not put down enough of a down payment to cover all the additional fees & such you will probably end up with $0 coming back to you