M y feet keep slipping whenever I take a back step. Then transfer your weight completely over the foot by ensuring that your hip is moved directly over it. This process is slow until your legs develop more power but it gives you more control, especially on slippery floors. I have trouble keeping up with fast music. You might need to relax a little.
People tend to move slower if there is tension in their bodies.
Another possibility is that your step size might be too big. If so, then you should dance with smaller steps, at least until you build up enough power. In the tutorial it's taught as ninety-degree turns. I don't feel confident or safe dancing in heeled shoes. The answer to your dreams is the toe lead.