Or try what I did, and which Sue beat me to posting about (😁), which was simply to change the properties of that piece of floor to be the same as the wall you'd already drawn:

There's always more than one way to do something using CC3+; you just have to hunt around to find it sometimes!

Looking at your PDF sample map, it seems as if what you may need are just hexes with three different fills to duplicate it. Two of those are terrain fills, the other is simply the flat colour representing open terrain (I think). If so, you can easily create those in CC3+, providing you have suitable bitmap fills available (either custom fills from the publisher, or ones you think will be suitable from what CC3+ assets you have available). All you need do is draw a hex using the hexagonal snap grid, and then change its fill style, then copy and paste that hex exactly where you need, again using the snap grid.

The river and coastlines may be trickier, because those are all obviously freehand on your sample map (I've drawn this coastline myself before, although for the ancient period, so I know it's not easy!). However, there is a trace option using CC3+ drawing tools that is able to at least approximately follow strongly-defined lines (that is, lines where there's a good degree of contrast) from a bitmap image (such as a JPG) imported into your CC3+ map. (Note though that this is separate to the Trace command the tools allow you to use when drawing with one in CC3+, because that needs a line already drawn in the CC3+ map to follow, not something on a separate image).

Sue's advice is good if you wanted to draw a map with a lot of different terrain types particularly, but those terrain symbols do seem rather different to your sample map's appearance. Hopefully though, some of our comments here will help point you in the right direction!

[And don't be so modest @mike robel 😁!]

It is fairly straightforward to draw hex maps using Campaign Cartographer, providing you have access to one of the hex-map styles. I did a series of small test-maps in such a style back in 2023 here, where you can see both the snap-grid placement of symbols and terrain hexes, coastal shading, and, by scrolling further down the page, some samples where I redrew the coastlines by-hand. Adding roads and river lines would be fairly easy as well, as they're simply coloured lines of whatever style and thickness you prefer, and which can be drawn freehand, or using the hexagonal snap-grid.

@mike robel here has created a number of historical wargame hex-maps. This is his most recent topic on the subject. He can doubtless advise further on the subject, given many of his maps are based on real-world examples.

Obviously, we need some entwined knotwork wyvern designs for the furniture, but it's otherwise looking wonderful so far 😁😉🐲!

Cthulhu City is a great period style, though the final map of the three above seems a little bright and almost sunny for a Vampire City, perhaps? 🧛😎