The hydrocortisone is worthless for your condition. The cortisone used in this case requires a prescription, so you'd need to throw modesty out the window to obtain it.
Simple manipulation will do the trick as you've already proven. You quit before the job was finsished. Plateaus in which nothing is seemingly happening are part of the progress. Cells need time to grow, and this is when they are growing. If tension is not applied during this crucial, the skin will stop production of new cells and revert to its former size and shape. You must work through this.
The exercise you have done is the right one as evidenced by your progress, so continue doing that, but don't miss sessions or give up this time.
No, your condition is actually not severe at all. Many guys who visit here can't retract at all, even when flaccid. You have a good head start.