You've had this snake for about three weeks - right?

If this is incorrect, then disregard what follows:

First, there is no such thing as taming a snake. You can acclimate a snake to your presence, to his surroundings, etc. but any things outside of the routine, or outside of what he has been acclimated to will result in defensive or stressed behavior.

Your boa is not striking because he's mean - he's striking because he is stressed. Bringing him home, putting him in a new enclosure, rearranging his environment and going through a shed are all individual stressors. Leave him alone for a while. Change his water if necessary, spot clean when applicable, but maintain routine. For the most part, stay away from his cage.

After you give him some time to acclimate and he begins to show signs of settling down, start out with short handling sessions. If you are afraid of being bitten and show nervousness or hesitation, use a hook or a glove to remove him from his enclosure. Start out with brief handling sessions, letting him move freely through your hands. Don't plop him on a couch, the floor, show him off to your friends, walk around with him, etc.

I picked up a cribo from Delta Dash last summer, after I got the snake home, I held it for about 30 minutes examining it and marveling at how well-behaved and calm it was.

That was the last peace I had with that animal for 5 weeks. It's very common to handle an animal with no issues at a show, a pet shop or a breeder with no issues and then have that same apparently calm snake do a 180 on you when you bring him home.