I don't think it's too shabby for a first attempt! Looks pretty well lined up, and the town layout is very original. Obviously it isn't finished so it won't too amazing now, but give it a bit mroe work and it'll turn out pretty good!
Note: Just a bit of advice - a little wooden fence realistically wouldn't look right alongside a big city palace
![Stick out tongue :p :p](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
I'd recommend using the walls that come with the castle tbh.
Here's a guide to deleting:
Erasing can only be done to objects, although any last action (and only the last action - i.e. last click on the map) can be 'undone' by pressing 'Ctrl + z'
You must remember that object tilesets are made up of many vertical 'objects'. To delete them, select the 'Ers' tab, and you can remove them by clicking on the square when the actual vertical object was placed (when you place an object tileset or object strip you will see a lot of grey rimmed squares - you have to delete them to delete the objects slips).
You must also note that the map editor doesnt automatically refresh, so you have to drag a palette over the area which you've erased or editted to see if a change has been made.