My iguana lost his tail and now hes aggressive?

I bought my iguana from petco and he was very calm and healthy looking. He would let me pick him up and walk around with him on my shoulder. Then like three days later he was sitting on my shoulder and he got scared and tryed to jump. I didnt want him to get hurt so i grabbed him and i was only able to grip his tail. As i tried to get a hold of his body he dropped his tail. Now he gets very aggressive when i go to pet him or hold him he whips his tail, lunges at me trying to bite me, and scurrys around. when i do get ahold of him he sometimes calms down but he sometimes trys to wriggle away. I try reading a book to him outside of the cage so that he can get used to my voice and hes okay with me doing that. I also put my hand up on the screen near him to get him used to my hand and stuff and he is also okay with that. He doesnt mind me in his cage as long as i dont go near him. Im trying to get him to feel safe around me but i am afraid it will never work. Can someone please give me some information as to how to regain his trust?