Did I ruin the cat introduction (introducing 4 month old to 2 year old)?

[Rachel73669]

I'm sorry for probably asking a question that many, many people ask, but once again in researching this topic I haven't found anyone with a similar background, and I know there are lots of people that know more about this than me! So hopefully you're willing to make a reply!

We got another kitten yesterday. He is 4 months old, already neutered, from the Humane Society. We have a 2 year old at home, also a neutered male. Sounds good, right? I've never had 2 cats before, and needless to say, made some very rookie mistakes. We had been planning to get another kitten in a few weeks, but after seeing his picture online we made a spur of the moment decision to pick him up yesterday... on the way to my other cat's vet appt. My 2 year old doesn't like the vet (who does), but he does okay, no hissing or growling, just hard to get out of the carrier. Well on this stressful day he sees the other kitten, smells him, in very unfamiliar territory, and was very unhappy about it. Not aggressive, but very freaked out. Then he was hissing at the vet, which he doesn't usually do.

So I'm very afraid that I've already messed up the introduction. The kitten was allowed to roam when we brought him home, but at about 11 PM they were separated, and the next morning we made up a separate space for the kitten who has been in there all day. He meows for stretches, and my 2 year old can hear it, but he has shown no interest in sniffing the kitten through the door. My 2 year old seems to be eating, drinking and litter boxing normally, and a couple hours ago I finally got him to a point where it seemed like he was playing with me normally. The only thing that seems out of whack is he is not happy when we pick him up, when before, he would tolerate it for several seconds. Now he cries and wriggles out instantly.

I know it was stupid to have them see each other in completely unfamiliar territory. I seriously would kick myself if I could, and I feel sick to my stomach for stressing my cat out so much. Is all hope lost?