Your ppu (pixel's per unit) is probably set wrong for the sprites. Each cell is 1 unit, so you want your ppu to be set such that a tile completely covers your unit area. Say you have 32x32 pixel tiles, you then want 32 ppu. Most often you just have to set your ppu to match the pixel size of your tile, unless you're dealing with extra large tiles that span over 1 tile (say a tree, or building, or the like). You'll find the ppu setting under the sprite import setting. It defaults to 100.