How do I fit map tiles to the grid seamlessly?

I am new to roll20 map making. I have bought several map tile packs by Gabriel Pickard. When I put the tiles down they do not fill the grid. there is empty space on all sides so I can not fit the tiles together seamlessly. Nothing fits together. Is there a tool or setting I am overlooking?

Are the tiles sized so the grid is at the right size? Generally the once you have the grid correctly sized they fit right next to each other. If there's still space you can place things without snapping to the grid by holding the alt key to place it anywhere. You can also right click and select the option "is drawing" to have it never snap to the grid.

Also, not all of Gabriel's sets are intended to tile. Which sets are you using?

If you place a graphic on the token layer from the marketplace, it will come in at 1x1, the most common usage. Oon the map layer the default is 3x3, which is not terribly useful. There are plans afoot to have assets from the Marketplace come in at pre-specified sizes (this is harder than it sounds). Artists have been required to input dimensions for a while now. Most of Gabriel's stuff is labeled with the number of 5 foot squares it is supposed to occupy. You may need to widen the Art library tab to read them. Right click on the graphic, and you will find an option to resize according to pixels or units. For Gabriel's stuff, choose units and plug in the numbers from the title. It should pop to the ppropriate size.