Ok, now I can look at it on my home computer...

Well, first of all, that's a really nice map. Especially for a first try...


Now... lemme see what could be improved...

The first thing I notice is the weird thing outside the walls, it seems like the floor texture is reflected or something? Personally, I'd get rid of it, it is a bit confusing, I think.
Jack already talked a bit about how to improve your transition... I'd use these techniques between the sandy and the stone floor, to try and make it look like some of the sand is spilling on the stone. Alternatively, just put your stone floor on a layer above the sandy one, then create a new layer in between and go over the transition with a black brush. Gaussian blur (7 pix, shoud do) and reduce this layer opacity to 85%. That way, the last stone casts a small shadow, making it look like it is laying on top of the sandy floor...

There seem to be a solid wall between the two stone floors, so it looks a bit weird to see the corridor continue... I also don't really like how the stone floor look on the bottom right, I feel like the lines of the stones conflict with the grid. I think that, personally, I would reuse the other stone texture, it looks great. If you want some change, you can tweak the colours... I think it would look better.
You can also redo the trick with the black blurred outline, if you want to suggest a step between the two floors...