If you'd like to make your work appear a little more gritty, I might consider changing the way you draw the forests, in particular. That seems to be an obvious source of the "bubbles" mentioned by another poster above. Some jagged, scary-looking trees might be hard to draw, but would look really good. Just experiment with different forest designs, I suppose.

I would also have drawn the bridges in the Itania map using only one line (some appear to be done this way, but others are drawn with two lines, making them look really big). I think proportions are quite important to a gritty look, simply because having things be too big or too small evokes the same feeling a cartoon would. Humor. A lack of realism (think of the political cartoons that portray politicians with big ears or noses).

Beyond that, you might try experimenting with your hand-writing. That might be difficult if you naturally write that way, but maybe some sharp edges and fewer gradual curves might make it look less cartoony. Just don't bubble your letters

So those are, potentially, some ways to reduce the cartoonish appearance without changing your medium.