what to do if i put the wrong gas in my car

I would live with the problem until it is down to a half tank and then top it off with premium. If you are worried about it add some octane booster like this ----

what gas did you put into in by mistake and what is the recomended grade/ octane....and does it rattle only under a load????

Grade of gas is not likely to make a noticeable difference unless you put your foot deep into the gas pedal. I would think you likely have other issues.

Yeah, a lower octane gas is not gonna cause immediate problems- how long since you had a major service on that Bimmobile?

You likely won't have an instant problem because of the gas being too low octane, but you should probably just add in premium gas. Octane booster wouldn't hurt, either. Heck, you could probably throw in a bottle of fuel treatment/cleaner, too, because depending on how long it's been since your last treatment, that could be an issue here.