My son and I are installing engineered flooring, and after installation of several rows we now have gaps in one section of the flooring on the butt end of the boards. I think the main problem was the floor floated away from the shims while we were working and as we pressed the floor against the shims in one area it pulled from the other. Is there a recommended way to fix the gap problem?

You can either removed the gapped boards and relay them tight OR putty the gaps.

How well does putty mask large gaps? We have gaps in our floor ( i believe its maple.. but i'm not sure) that are about the width of nickle. does the putty make it look natural?

If you look for it it will be noticeable. I've actually found Pergo sealant to work pretty darned well filling larger gaps and it does comes in a color resembling Maple. One full caulk tube goes a long way. Costs about $ 8.00.

Wait, if it's a click together floor sometimes they can be kicked into position. Don't kick with hard soled shoes--clean sneakers work best. Be careful when kicking as it could jam the whole floor up against the baseboard or wall on the opposing end.