Two things -
1. Make sure your corners are at least 3 pixels long on both sides. Dragon needs at least 3 tiles to make a proper transition.
2. Dragon can't do NW corners properly. Its a limitation of the way Dragon works, it does not support 3-way transitions and so doesn't create proper NW corners. Those you need to fix manually. But see here for a way to manually fix your NW corners using Worldforge or some other map editing program by lowering the terrain tiles (the screenshots are missing but hopefully you get an idea of what he means):
Ryandor.com :: View topic - Tweaking Mod11 coastlines in Worldforge
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-= HellRazor =-
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