Prep is 80% of the finished product.
400 grit wet dry to start with. Than use 600 grit to feather into the exsisting paint. Look at your work from every angle you can, while sanding, so you get a good idea of when you’re through all the clear and are into the base color.
Depending on how much sanding you can handle, you might want to sand out the 400 and 600 grit scratches with 800 or 1000 grit. Up to you!
Matching new paint to exsisting paint can be one of the biggest pains a painter faces. Did you get matching chemistry color and clear and does that chemistry match or come close to the original chemistry used by the manufacturer? Also if you shot the clear on a humid day, wait for a dry day, that is if you’re going to attempt another clearcoat.
I’d suggest getting a scrap piece of metal and shooting it like you would shoot the car. That’s what the pros do when matching paint.
If you want a perfect looking shoot, you have to be willing to put in the time and elbow grease to get it right.