This is a known issue caused by the effect of scaling a tiled object. Basically put, when you scale the tiled background, spaces may appear because the images making up the tiles scale as well and may not scale the same.
Basically, if you scale a 100 x 100 object made up of a tiled 10 x 10 image down to 95 x 95, the 10 x 10 image has to scale down to 9 x 9. Pixels don't have the ability to show just half a pixel. This means the first 2 tiles will be right next to each other then there will be a 1 pixel space between the next. This isn't an issue in C2, it is the nature of how pixels work.
C2 has a way to deal with this by implementing "Seamless Mode." If you had read through the manual, you would have found the information about this here:
https://www.scirra.com/manual/172/tilemap
I hope that helps you out and good luck with your project.