Ruined My Cats Introduction! Help!

I adopted an amazing cat about a year ago named Moira from the Humane Society. She had been surrendered from a home with 6 other cats and besides her being quite the spoiled diva, everything has been awesome. Super affectionate, head bunts us frequently, even sleeps on a pillow above my head. The only time she's ever even hissed at anyone or anything is during car rides. She even seems to enjoy getting her nails trimmed. I guess I'm basically trying to say she is super sweet and docile, even allowing toddlers to play with her.

But here's the fuck up. First off I was ignorant in how to introduce cats to begin with because we'd never done that when I was a kid and I don't remember there ever being issues then so I didn't think twice when adopting a gorgeous kitten today.

When I first brought her home I expected some hissing and Moira to hide as she tends to be a primmadonna but she is PISSED. Now that I've done research I realize how badly I messed up but now I don't know how to fix it.

The new kitten (Botan) seems to be doing well since bringing her home from the Humane Society and staying pretty much glued to my side. Apparently she was dumped at the river at 3 weeks old so I believe I'm probably the first human to have the time to give her the true love and affection she deserves. I still keep trying make sure I'm giving Moira love and affection (lots of treats, reassuring and petting her when she seems to get aggravated and hissing, etc) but now she's seemingly mad at me too. She hasn't bitten any of us but she has swatted my ankles and hissed quite a bit. Also, earlier she went to her cat box and threw a temper tantrum because Botan had used it. Besides worrying that I ruined any chance of them being buddies, I'm terrified of confrontation since Botan still has stitches from being spayed.

Thus far I've allowed them in the same room with supervision and gave each a cloth that had been rubbed on the other so they could exchange scents. I plan on getting another litter box tomorrow and am for sure going to separate them when no one's home but what else can I do to make this transition easier for both of them? I don't really like the idea of keeping one or the other locked up when someone's home to watch them but I realize I may have already done irreplaceable damage to their relationship and am really willing to try anything to make my babies happy. I've already fallen in love with Botan so I'd hate to rehome her but I also don't want either cat to live in constant stress because of my irresponsibility in doing proper research.

Here's a pic of my gorgeous girls: https://imgur.com/gallery/Jyi19