One thing that I have noticed is that often when I inject, I will know right away when the injection has caused a trauma that will lead to a bruise. You all know the feeling, that awful stinging. When that happens, go right to the fridge, grab an ice cube and compress the injection point. A bruise forms from bleeding, and the bleeding stops within like 30 seconds. If you apply cold and compression to the injury site in those critical 30 seconds, you can markedly minimize bruising.
Usually, I just do the ice trick cause it hurts, but then again, look at my face, I am a total wimp.
ps. It may well be too late for a normal registration, but there are always exceptions to rules. Go right to the school registrar personally. Seek a meeting directly with the registrar and plead your case face to facce. You might be surprised at the result. Think about it.