I have a jet black E90 320d. The car has a few minor scratches here and there. I have some car plan t-cut scratch remover, I think this is mild t-cut. I have used this on other cars with good results. However, when I recently used in on my black bmw the results were awful. Residue was being left and the scratch appeared worse, it was leaving like a smudge around the scratch. I cant get this off either. Any ideas of whats wrong ? What should I be using ?