PGE1 injection: painful, but still not rock hard

I’m a beginner of PEG1 injection. So far my highest dose of PGE1 is about 28mcg. I felt penis painful as discussed in the forum, but not rock hard state.
My question is, should I increase dose until rock-hard erection state?

Here is my injection record:
1) 2.5 mcg
2) 5.4 mcg
3) 11.6 mcg

The above 3 injections are from one set of caverject.
From 4th injection, from Dr. lab.

4) 8 mcg
5) 18 mcg
6) 28 mcg

I feel that 28 mcg dose makes a roughly 85% erection.

Thanks for your opinion.

My purpose is penis enlargment, not ED improvement.