I accidentally put regular gas in my flex fuel ford focus?

I can usually go a week without having to fill up but after using the regular gas i can only go a day or two on a full tank before i have to fill up.

I thought if i let my tank go to empty (even the refuel light came on) that would help, but it hasn't. What should i do to get my gas mileage back to what is was before?

I don't know, but one thing you don't want to do is run the tank down empty as it may draw sediments into the fuel system, fill up when 1/4 full.

Flex fuel means it will burn anything. You could buy a bottle of octane booster at the parts store. Otherwise, just add premium as you burn what you have in the tank.

Regular gas should cause no more than a 10% to 15% drop in mileage. If your mileage dropped by half there's something else wrong and you need to have it looked at if more than 2 tanks of premium does not take it back to normal.