The scalp pigmentation tech should have NEVER lowered your hairline below your natural line. This is because pigment "cures" differently in scalp skin than it does on the facial (forehead) skin. The color will never match and you will end up with an off-color stripe around the front of your hairline. So many techs are more interested in their pocketbooks rather than the customer's own best long-term natural look. So they readily make rash decisions. You should have been advised of this. So you are correct in getting it lasered removed.
As for the redness after 12 days, that is highly unusual. While HT scarring easily becomes irritated with scalp pigmentation, the redness should have dissipated within 3 days at the very most. The redness along the frontal hairline can also be because the tech "buried" the needle into the forehead skin that never should have been tattooed to start with. Yes, get to a doctor, as perhaps there may have been a sterilization issue.