Montserrat's pretty small. It's less than 40 sq miles. Depending on what size you're looking for, create a custom map in CC3 instead of using one of their templates, so you can set the size yourself.

File > New, then click on "Overland Maps" and make sure you select "Decide settings myself." Then click next. Choose whichever style you like on the next screen (such as "CC3 standard overland") and click next. Here's the important part: the next screen asks for map dimensions. Unless you've previously changed some settings, this defaults to miles! So if you want a small map, maybe an island 2 miles by 4 miles at the widest points, enter something like 5 x 5. I like to add in a scale, so click on "Bottom Left" on the same screen (or whichever corner you want to put your map scale in), select one of the map scales, and click "OK." Then click "Finish" and you should be good to go. This will give you a properly scaled playground to mess around in.