This issue indicates that you are not able to select the street properly, and when CC3+ doesn't detect a street being clicked, it just does a straight line instead.

Make sure that the street is not on a frozen layer.
Make sure that you click on the centerline of the street when selecting it, this is easiest to do when you are not zoomed too close since the pick cursor is larger in relation to the street.

Myktolos castle have now been added to added to the atlas. Thanks for the contribution.

Myktolos Castle

You'll never be able to upload that to Roll20. Image that size gets into the Gigabytes, and Roll20 only allows for files up to 10MB (5 for free account). That export size is just plain crazy.

You'll never be able to upload that entire map in battlemap scale to Roll20.
What I recommend is to upload a smaller overview map, and then do battlemap-scale maps of the areas where combat will take place, or other interesting features exist.

Note that if you really want an image that size, the only option is exporting in tiles. For that, Annual issue 129 is perfect for the job, which I used to export the City of Sanctuary. But realistically, you don't want to do that with this map, as you won't be able to use it as you are planning anyway.

For a basic export in CC3+, about 10kx10k is the upper limit. Depending on the map, it can be pushed a bit further, and some complex maps cannot even reach that, but it is a starting point for the max size.

People have different ways of doing things. Myself, I prefer to export the the CC3+ landmass directly from FT (as in the video).

Posted By: Stephan72My problem is now figuring out how to customize the map now that I've got it in CC3+.

Change Like Draw Tool is your friend here.

Just open the existing catalog files in CC3+ (open them in the main window, as a map, and not just in the symbol catalog window).

Now you can use Import png's to import new images, or if these images are already defined as a symbol in another symbol catalog, open that symbol up in the symbol catalog window, and click once on each symbol you want to import. When done, just hit save and you're done.