Only say what's bolded. You are super excited. When you say the 'oh hey..' line, you're supposed to be confused. You've never met Tiana before.

“Ava-Chan!” I hear a girl call. “Ava-Chan guess what!!!”

“Iku-Chan!” Iku Akiyama. She has long blonde hair. She’s the co-captain of the cheerleading team here at Kanayama High, along with Ava. “What is it? What are you so excited about?”

“There’s this new guy and he’s super super cute!!!” Iku exclaims. I wish I could share their excitement. Instead, I fake it.

“Oh my gosh, really? Where is he?” I ask her.

“Oh. Hey…”

“Tiana-Chan,” Ava says.

“Hey, Tiana-Chan. Good to meet another one of Ava-Chan’s friends. Anyways, he’s in the office but the bell is about to ring. We can find him later in the courtyard during lunch.”

You're still really excited. Make sure that the 'what was that' line sounds confused.

“Ava-Chan! Tiana-Chan!” I hear Iku’s voice yell. “Ava-Chan! Over here!” I look over and see Iku waving to me and Ava. We walk over. “Guys! He’s sitting down right over there!”

We look over and I see Akihiko. My heart starts beating faster and I can feel my face getting red. I must make him mine. “He’s so cute!” I hear Ava say. I feel a burning sensation in my stomach. I glare at her. “What do you think Tiana-Chan?” She looks over and I put a smile on my face.

“He’s okay but soooo not my type.”

“I wonder what his name is?” Ava says.

“Go find out,” Iku says and nudges to her.

“Akihiko Sakamoto,” I mumble. They both look at me all confused-like.

“What was that?” Iku asks.

Sound betrayed and heartbroken. Also sound mad.

“Oh my god Ava… You ditched me and Tiana for old-man-sex?? Don’t talk to me, you slut…”