cortizone injections

A small pimple showed up on my chin near the end of my accutane treatment.  It grew overnight and the doctor told me it was a cyst.  The doctor injected it with cortizone, which reduced the size of the cyst somewhat, but not to my satisfaction.  The next week, they injected it again and more of the swelling went down, but not all.  The third injection (two weeks later) brought the cyst down to almost gone, and then a week later, it raised again.  Currently, the cyst is small, but I am tired of having it on my face!  I have an important event very soon and I don't want to attend it looking like this!  This wasn't a large cyst to begin with, and I am on accutane, so it makes no sense to me why this thing is so stubborn.  My question is, would you recommend a fourth cortizone shot?  I believe it would take care of the remaining bump, as each of the three previous injections reduced it in some measure, but I have been told that I risk atrophy.  Please give me advice.