You are no longer a
pureblood, one more or one less booster doesn't really matter anymore in the grand scheme of things.
Also, MOH will keep spamming you with 'reminder' or 'invitation' smses until the day you die, and you cannot opt out of this. You have already given them your
information and
consent when you filled up the form to get your first two jabs in 2021. Good luck!