Agressive 4ft boa constrictor?

So i got a boa on thursday he was a bit grumpy so i left him till friday and i got him out, he was fine then he went a bit wierd and striked one of the thermomaters when i was putting him back in. Today he was hissing and didnt want me to pick him up, so i fed him. But how am i going to build up the trust with him? Hes about 4ft long and always wants to bite me so it seem. Any tips for getting him under control?