By being a prefinished floor there is really no way to fix the gaps. There is a way you can make them look a little better. It is best if you have good carpentry skills. If you have access to a table saw follow the following steps. Use peices of your flooring to do this. Set the blade of the table saw to 7 degrees. Set the fence so that you only cut a sliver the thickness of the 3/4" hight of the wood. Flip the wood over and set the blade to 0 derees. Keep flipping and changing back to 7 degrees until you have more peices than you need.
To install these slivers cut them to length, add glue to both sides, and put the peice in the crack. Tap it lightly with a hammer. Use a utility knife and score the sliver lightly on both sides. It will then break off easily. When the glue sets up you can sand and stain to your liking. You can then put poly on to match the finish of the floor you have. Try one spot first to make sure you like this. Don't forget to tape on both sides of the sliver to make sure the poly does not go onto the finished wood.
To install these slivers cut them to length, add glue to both sides, and put the peice in the crack. Tap it lightly with a hammer. Use a utility knife and score the sliver lightly on both sides. It will then break off easily. When the glue sets up you can sand and stain to your liking. You can then put poly on to match the finish of the floor you have. Try one spot first to make sure you like this. Don't forget to tape on both sides of the sliver to make sure the poly does not go onto the finished wood.