Broken foot not healed

I broke my foot 7 weeks ago. I broke the side of my right foot stepping down stairs on the side of my foot, instead of the flat of my foot. I have been in a walking cast for 7 weeks. My xray shows that it is not healed all the way. It is about three quarters healed. The doctor says it may never heal and I should walk on it anyway because otherwise my foot and ankle may become frozen. When I did walk on it without the cast, it was very painful and became swollen. I don’t feel right about walking on a broken foot. Is what he says true? If I just leave the cast on for a few more weeks, will it heal?