There are numerous scratch removal products that are widely available. They work if the scratch is in the clearcoat and not through your paint. They are all a basically a paste that contains very fine pumice that acts like 1500 grit sandpaper and smooths out your clearcoat. The key is to wash your car clean first then use the scratch remover with a clean microfiber cloth and work slowly on the scratch in small circular movements. I have used 3M Scratch Remover and Meguiar's Scratch-X both with good results.
If your scratch is through the paint, then try Dr Colorchip