GFI electrical outlet

So My house was built in 74'. An electrician replaced my basebord heaters with wall heaters for floor space. They are 220v. I wanted to replace the old dark brown plugs with white ones. There is one GFI that has 2 sets of three wire coming in. After that there is a light swith and outside lights. On the exsisting GFI one of the ground wires was not hooked up and the on one of the lines coming in. I went to hook up the new GFI and thoought the ground wire should be hooked up so I twisted it around the other ground wire. The outlet or the light switch didn't work.

Problem...I forgot which ground wire wasn't used. Does it matter which one I leave out? Is it a fire hazard?. The GFI is in a box used for 2 outlets maybe like a junction.