Get a split keyboard. I had the same problem until I switched to a Microsoft split keyboard. It forced me real quick to learn to type with the right fingers, because the wrong fingers don't reach correctly.

I learned it using typingmaster pro, a program for 30 bucks.

It starts by teaching you the keys under your index fingers. Then additional keys for your middle fingers, so on and so forth. It shows you which key is supposed to be typed with which finger. Of course you have to make sure that you use your fingers correctly.

I was already typing with five to seven fingers, but training with the program for about two weeks, everyday 30 minutes, greatly improved my typing, now I use 7-10 fingers. Although I still use my index in middle fingers to often.

See my other comment here.

https://news.ycombinator.com/item?id=9578463

Since I wrote that comment I discovered that the GNU typing program called gtypist appears to use an approach close to the one I describe there. You might try that one.

Whenever you find yourself typing a word incorrectly, delete and retype it. It will take some time, but that's the only way to lose the habbit.