Patience and a steady hand is what is required.
What you should try and do is fill in the scratch with the touch up paint and not cover it. Covering it, in other words trying to blend the paint just does not work. Step by step, using a cocktail stick to apply the paint, and allowing each coat to dry is the answer (use of a hairdryer can speed this up). Once you have enough paint in the scratch then leave well alone. Same applies for the clear coat, again do not try and blend it, you will just end up with a blop of paint.
Hope that helps.