The HSA custodian is not required to accept a return of mistaken distribution. To be eligible for a return of mistaken distribution, the distribution technically must have been made with the belief that the distribution was to pay a qualified medical expense that later turned out not to be the case. I think it would be difficult to convince the HSA custodian that a debit shown as coming from a gas station was thought to be for a qualified medical expense, but it might be worth trying.
Otherwise, just be sure to keep receipts showing the amount of medical expenses to which the distribution from the HSA is applied. Qualified medical expenses can be any medical expenses incurred after the date that the HSA was established paid out of pocket for you, your spouse or your dependents, although reporting HSA distributions that were used to reimburse yourself for expenses incurred in an earlier year can be awkward in TurboTax.
