Venous leak is very normal and just a part of the healing process. Now with only one set of nerves left, you may take longer, but hey, with where you are now, I'd say you are doing really, really well.
Your goal should be to take an assesment at the one year mark. There is a marked improvement for many guys at 9 months, then again at one year. It sounds to me as if you are well on your way to a total recovery. Many guys with both nerves do not get erections like yours at the 4 month mark. Congratulations.
Stop worrying. Be happy. You might try a constricting cock ring to help things out - unless is the band you are talking about an Actis Band? Then they are the same thing!
Paul