Doubting if impurity fell onto the toilet seat

I have a question regarding washing a place that is najis. I usually can see when this particular thing falls on the toilet seat but I know some water did flick off my hand when urine was on it. I washed the inner half of the seat, but was doubtful if it had gone onto the outer edge of the seat. I can usually see it if it falls on all parts of the seat, but because the seat didn't have anything on it I am still doubtful that it may have flicked onto the edge of the seat. My thigh also touched those places thats why I'm worried if it transferred onto me. I also saw something flick off my hand, but cleaned the floor because it felt like it hit the ground and not the seat. All of this is putting a lot of doubt in my mind? What should I do?