Need help, cant get primer right

[custexplorer]

I had some scratches on my bumper and I sanded it down to black, then taped and did two light coats of primer. The primer is bumpy and seems to stick out from the regular paint. So I sanded with 400 wet sandpaper to try to blend it more with the stock paint and it all came off. What can I do? It seems like one coat of primer is thicker than factory primer, paint, and clear coat combined.

 

[MONMIX]

*scratches head*

Okay lets just walk through this.
You have a scratch. Sand it out with 220 grit so it "feather edges" Meaning that is feels smooth to the touch and you cant feel where the paint starts or stops. Blow all the dirt off with compressed air. Now apply your primer is one or two thin coats covering the entire repair area. Let dry fully and sand smooth with 400.
This should yield the results you desire.

 

[catdaddy614]

you need to prep the area better.