You have to enable the DevTools, but that requires a $99 annual fee. If you can't afford gas, it's not likely you can afford that fee too. So it's kind of a perfect catch-22
Why would you have to enable devtools? Also, with just an unpaid icloud account, you can build, sign, and install apps to devices with an expiry time of one week.
It's better to just return it to a different gas station. Selling gas is more difficult than you might think because of rampant dilution/adulteration in the secondary market. Can't just go door to door saying "Hey I bought too much gas" or "My car only takes 93 octane" -- nobody trusts anyone anymore.
When you make a return without a receipt you generally just get store credit instead of cash. If you don't need some chips and tallboys, you can typically sell the credit to someone behind the station for .3 to .4 of the face value. That isn't great but since the gaming machines only take cash its a solid way to get liquid.
Just act normal and ask for the manager. Like the parent comment noted "probably very much worth the small investment in tools." Be sure to get one of the fancy black rubber hoses instead of the green ones so things look more professional.