I'd suggest you back up and
- Think about what makes "good" continents.
- Write an algorithm that can tell a good continental layout from a bad one.
- Refine the algorithm so that you can quantify how good a good layout is.
Once you have that in place, you can start to implement an algorithm which should be shaped like this:
- Generate crappy continents and then improve them.
For improvement you can try all sorts of standard optimization tricks, whether it's simulated annealing, genetic programming, or something completely ad hoc, like moving a randomly chosen edge square from whereever it is on the continent to the edge opposite the continent's center of mass. But the key is to be able to write a program that can tell good continents from bad ones. Start out with hand-drawn continents as well as your test continents, until you get something you like.