yeah forget about heel toeing for now. i mentioned it as a technique that can help you get faster, but you must be under control and comfortable driving without it. if you're already making mistakes that cause you to skid off the road, then trying to perfect heel toeing while you're trying to nail down your racing line will likely be counterproductive.
i was thinking, and i have a guess at what's going on. you are using the cars in front of you as guides for braking. my guess is that when you see them brake, you start your braking in a panic, and slam on the brakes. this causes you to skid, and you're not going slow enough by the time you have to turn. so likely you are still braking with locked brakes when you begin turning, and this will surely send you flying off the road. be gentle on your brakes.
i think the best thing you can do is not to stress about how good you are, and just start hot lapping in a car you enjoy on a track you enjoy. if you're in the middle of a race, if you're at all like me, you start making more mistakes cause the pressure's on to go as fast as humanly possible. so take a break from that. pick your favorite car and track, and drive that combo a ton. i would suggest the lotus kit car on the demo track. the lotus is zippy, turns quickly, and brakes super quick. try to drive fast, but don't overdo it.
just enjoy the drive!
once you've got an idea of the capabilities of your car, and are getting fairly consistent lines, you can start trying to improve that, take it on other tracks, and take it online. then when you watch people, you can see what the differences in your styles are, and that will hopefully mean more to you at that point.
also check out guides on racing techniques from actual race sites. i find they impart a little more insight than most videogame resources tend to. tho i haven't looked at lfs's guide, if there is one.
here check this out:
http://www.nasaproracing.com/hpde/theline.html
more links at the bottom of that page