The 34-year-old bantamweight joined Babcock on the TMZ Sports TV show (airs nightly on FS1) on Monday ... where she revealed the lead-up to the Ketlen Vieira scrap didn't exactly go as planned.

"I'm still learning. I'm still growing. I feel like there's a lot of room for improvement for me. It definitely wasn't my best night in the cage," Kayla says, adding ... "There were a lot of things that happened."

"You know, I don't like to make excuses. I had to go to the hospital the week before I was like peeing blood and there was some stuff going on. So I don't like to make excuses, but I definitely wasn't my best inside the cage Saturday night. And I know I can, be better and grow from it."

Despite dealing with health issues, and fighting a very dangerous opponent, Kayla still won by unanimous decision ... though it was a somewhat competitive fight. In fact, Vieira even made Harrison bleed, something none of her previous 18 opps could do.

We asked KH what was going through her mind when she felt the trickle of blood down her face.

"Honestly, my kids can't come to my fights anymore because my first thought was like, 'My kids are seeing this.' And that is not a thought I need to be having when I'm inside of a cage. I don't need to be thinking about my kids watching me bleed. So that was my first though," Kayla explained.

"I went into like mom mode. I was like, 'Oh my God, I hope they know I'm okay.'" 😅

She was okay ... and now the question is what's next.

Of course, all four women atop the division were in action on Saturday. Raquel Pennington, the champ heading into the night, lost by (albeit) controversial split decision to Julianna Pena. And Kayla, ranked third, defeated Ketlen, ranked second.

Harrison will likely slide into the number one contender's position ... but that doesn't necessarily mean Kayla vs. Julianna (who don't like each other) is next -- 'cause Amanda Nunes is also in the picture.

We asked Harrison which fight she'd prefer ... Pena for the UFC title, or Nunes in what could potentially be the biggest fight in women's MMA history.

"I want both. Can I not have both?" Kayla asked.

"I want to win the title, give Amanda time to get back in shape and train. She can be training for me that whole time. I'll go f**k up Julianna real quick, and then Amanda and I can fight."