I had almost the exact same thing happen to my boa when I was a kid. It didn't matter what I did after he hit about that size. He was aggressive. I got bit multiple times pretty much anytime I entered his enclosure. I didn't care so much but my mom finally put her foot down and I donated him to a boa breeder that was happy to take him in. I would seriously think twice and then a third time about taking in a snake like that.
Regards,
B