I have to give my cat ear drops now & then. Like your cat, at the vet's she was fine. I get home and try it and she goes wacko.
The next visit at the vet's, I ask them HOW do they do it, because I need four hands, two to hold her down, a third to flap her ear back & hold it open and a fourth to administer the drops.
Turns out, there is a
procedure to approaching and holding the cat. I wish they had taught it to me.

But, I guess they learned it in Vet school, and it's so natural for them to do it now, they don't realize, we mere mortals don't know how to do it.
You have to approach the cat from
behind and come up next to him, so your whole arm is over his whole body, your elbow at his tail, hand at the neck, and then gently pin him down with your arm. Scruff him from that way. Don't be facing the cat, trying to do stuff. Administer from behind. If he sees you coming with the IV, he's going to go crazy & run & hide. I actually have to hide the cotton balls & ear drops so my cat doesn't know what's coming.
Also, your kitty is probably sensing your hesitation or nervousness about doing it. Remain calm when you insert the IV.