In that case, I think it is best that you put in a tech support request. You'll find the form on your registered user pages. They should be able to get you back up and running.

Since CC3+ always tries to open the last map on load, there is a chance that something has gone wrong with it.

First, to open CC3+, try to either double-click on another .fcw file on your drive, since that will open CC3+ with that file instead of your map, or rename your map file before starting CC3+, since this will cause CC3+ to not find it and will open up without a map (showing a black screen).

After that, you can try opening your map using File -> Open. If that crashes CC3+ immediately we know where the problem lies and can take it from there.

Was the original polygon properly closed? In CC3+, it isn't a polygon unless it is a closed shape (it's then a path), and if you try to set a fill style for a path, it is only applied to the line itself (And keep in mind, in a CAD based software like CC3+, being closed is a property of the entity, not just that it looks closed on visual inspection, there is a close path command by right clicking the explode button).

Your map is nice, but I would recommend you look a bit at your grass, the repetition of the texture is a bit much. This can often be fixed by adding more stuff to the map, combining it with other grass/terrain textures, or changing the resolution of it so it doesn't repeat quite as much. Also, maybe not use the same floor style for all the rooms. You can also use a shaded polygon to angle the fill in that stand-alone building to fit the direction of the building.

You don't need to make a new style, you should just make a new template for the style. Just make a copy of the existing one and edit your copy. The thing controlling the aspect ratio is the RESIZE map note, just change the contents from SCALE to STRETCH.

You probably have attach enabled (button lower right)