The key thing with touch-up paint like you show in your picture is to make sure it's fully dried and hardened.
Here's the issues to overcome,
Removing all the scratches in the surrounding clear coat
The touch-up paint will tend to be softer than the factory clear coat finish, what this means is sanding marks will buff out of the touch-up paint quickly and easily. Not so with the factory clear.
Careful not to heat up the touch-up paint and pull or yank it out of the scratch
This normally happens when using a rotary buffer but it could happen with another tool too. Here's what happens with a rotary buffer, you start buffing out your sanding marks and the remove quickly out of the touch-up paint. The don't remove quickly out of the surrounding factory clear so a person continues to buff, maybe even start pushing harder on the buffer to try to get the sanding marks out.
The panel heats up and with it the touch-up paint and the buffing pad will literally grab or yank out the touch up paint or most of it.
Now you'll be back where you started only now you'll still have the sanding marks in the surrounding paint and because you've sanded this area it will now be thinner.
I think I added this little tidbit of information to Richy's excellent write-up on this exact topic,
Key Repair-Step by Step Procedure
See my post #28
Another option is to take one or two fingers and rub "most" of the sanding marks out along the side of the scratch by hand. That way you're not running the buffing pad over the touch-up paint while trying to work out the more stubborn scratches in the surrounding clear coat paint.
One thing I've been typing about rock chip repair and scratch repair projects like this is,
You can make touch-up repairs as simple or as complicated as you like. Sometimes doing more and more steps won't equal better and better results.
