Vet Disaster!

We got Merlin just over a week ago, hes a beautiful 4 month old Eclectus. He is our first large bird (we have a lovebird who hates me and loves my husband) so were still learning how to take care of him. He came in on a 4 hour flight from a breeder and was understandably scared but he came out of his carrier the next morning and began eating/drinking regularly. He wouldn't quite let us touch him (he was tasting/lightly knawing on my husbands finger) but I felt it would get better.

Then we took him to the vet the next day to ensure he was in good health and get some tests run. He was in a towel the whole time and was making screaming noises. He was pretty scared to say the least and since then he has been showing signs of aggression toward us. He will fluff out his feathers and open his wings threateningly toward us if we put a single finger inside the bars of his cage.
He is still eating/drinking regularly and making more noises which I hope will soon turn to actual words. So he seems physically happy/healthy but I'm afraid he hates us, we were there when they were getting his blood and I held him in the towel for a bit because the vet handed me him in it so I thought it was ok. The breeder said the towel is super frightening for them and I feel so stupid for not realizing it. The breeder seems concerned so now I'm freaking out as well!

Has anyone else had these issues? I know it might just be a matter of time before he warms up but I don't know how to get him more comfortable besides trying to entice him with treats/talk to him/offer a single finger in between the cage bars in a non-threatening way.

I haven't had this issue, but I can still maybe give you a little advice. In case he has to be toweled again you should start getting him used to towels. Just have one nearby the cage where he can see it or if he's out and playing you can put one next to him. It will probably just take time for him to get used to you and stop being afraid. Keep offering treats and see what happens after a few days. Patience often helps a lot in matters like this. He might just not be comfortable with new people, especially since the vet incident. Most likely, though, he'll get used to you in time. Good luck!

ok yes ive had this and still get it, he is telling you this is his home and to stay out of it, all you can do isopen his cage let him come out on his own, it will take time, but once he has settled and is at peace with his surroundings, he will settle, the more you handle him the more he will settle , just when ever at his cage just put your face up to bars talk softly to him and over time he will allow you to put fingers in , the many thing is it sounds like he already has you bluffed,if you pull away when he goes to bite or you show any fear , he will have it over you for life, you must train him to not bite, and let him no its not ok for that behavior, and that you are the boss, well at least try to be the boss lol.