Is this normal to have these gaps on the mount or do I not have the correct one? It’s a Dewalt DWP611.
If the router is tight, gaps on the side is fine. Its a 69-72mm range that fits, to accommodate the Dewalt and the Bosch Colt. Clamping is done by the front plate and rear edge.
I thought 1.5 kW spindles were 65mm in diameter which will definitely need a shim. If you have a 3D printer, there are lots of shim files. Here is one I made so I know it works.65mm adaptor for RoutER11 and Makita (plus makita clones) to Openbuilds router mount by cgmllr100
There are tons of 65mm spindle mounts available on the internet. Sadly, few have the right hole pattern for 80mm extrusion. I wish Openbuilds would sell the shim that comes with the RoutER11. Hint, hint. You could shim it with aluminum long enough to cut a more precise shim out of aluminum stock.
Four years ago, when I started using my 1000x1500 machine, I also ran into the problem of the mount being too big. I bought a Makita router at the time and it obviously didn't fit in the mount. I then solved that problem by buying a piece of drainpipe with an outside diameter of 80mm. There I sawed off a piece of 20mm wide and sawed it in half again. I glued it inside the mount with contact glue and it has been there for four years now and works fine. If you come from the Netherlands you go for cheap.