A lot of the main problems have been pointed out by alias, ghost and slayer, I'm not gonna repeat these, but there is one I would especially like to tell you:
Mapping is not filling a quad. It's something I very often see with new mappers, and I did the same in my beginnings. You shouldn't create your map on the editor, that's important. Design it like you want with a pencil and a sheet of paper then reproduce it in the editor, and rearrange it later. It looks obvious you have started from a quad then tried to put some blocks onto it. If you would have used the pencil to draw and imagine, you wouldn't have done something so quadratic.
Again, it's nothing bad, it's absolutely normal, and to be honest your map is a good start.
Last advice, not to improve your map by any means, but you save you some time: right click on a tile, and click "Game tiles" then "Collision", it will make everything from this tile solid, so you won't have to fill it manually
Not Luck, Just Magic.