Man, that's a brutal lesson to learn the hard way. How big of a patch are you looking at cutting out? Ryan_sanchez is totally right about the dust and the finish. When we had to do a small fix like that on a job, the dust coated every single tool in the truck, and the new concrete never looks the same as the old stuff. It always ends up a slightly different color or texture, like a permanent reminder of the mistake. You'll be looking at that spot every time you walk in there.