I got an ink card pad on Amazon for a couple bucks. I ordered a ton of the fingerprint cards for free from the ATF mailing center. I just sit down and do my own fingerprint cards everytime I'm going to submit a form. I also just take a selfie in front of a white wall for the picture and print it off 2x2". I have submitted about 5 forms like this with no issues.
Do you have the link for the ink pad?
On the box that requires the signature of the official taking the prints, I assume that they didn't have a problem with you taking your own prints; correct?
Took me like 5 tries to get two good copies last time. If I can roll them once and then keep a scanned copy on file and just print on free cards from the ATF after that I think it will save me time.
I'm thinking that practicing on a blank piece of paper several times might help rather than the first attempts done on cards that you've either paid for, or got from the ATF.