Loosen the servo mounts, and with a little bit of wiggle, they should, maybe with a little bit of coaxing, slip right into the servo's mounting tabs. Those extra raised areas on the servo mount are there for supporting the servo better, they keep the servo from moving around on the screws, and the rubber grommets (that came with the servo) are not needed.

The fit and finish of some components is not always the best. The servo's mounting tabs/ears should sit flush on the chassis servo mounts. This is another place a rotary tool is helpful in the hobby.

I always put my servo mounts on the servo before putting the servo in the chassis like shown in the manual.

http://www.ecxrc.com/ProdInfo/Files/...nual-MULTI.pdf