Take it easy on this tank.

 

I'm sure your car won't be hurt by the one tank of regular; don't sweat it.
Once, just once, I filled mine with the highest octane Sunoco (usually use Shell premium - they used to call premium 'ethyl', you young guys! - and it ran horribly. I wasn't sure if it was the type of gas or just a bad batch.

 

too high of an octane can be bad too. as it burns too hot.