What Are Effects Of Taking Extra Dose Of Metformin?

I had a CT scan with dye yesterday. I fell asleep on the couch last nite and went up to bed, first taking my meds (incl 1G of Metformin). This morning I took my previously laid out meds which incl another gram of Metformin. Ooops! It's Saturday today and I don't know what to do? My creatinine level was normal (1.0) before the scan.