Yep... that map of Istarnia on Obsidian Portal was one of my first photoshop maps. I just cloned black and white symbols from other maps I liked -- stealing a mountain here, a forest there... and then painted it in a layer and multiplied it so the black lines showed through...

After that I found Cartographer's Guild and realized how much cooler maps could be with a little effort...

and now i have been spending crap loads of effort, likely reinventing the wheel a bit due to my lack of skill at following instructions in tutorials... ah well, at least folks seem to dig my world map...

one thing you could do for your sea texture is have a faint halo around the land to suggest shallow water... there are likely multiple ways to do this, but i just had the land as a layer and gave it a glowing edge for mine. other than that, your colours and textures are just fine... and you could even do well without the glowing edge...

good luck and happy thanksgiving!