What? You think Barry was kissing girls before Elsa? For him that was th biggest kiss he had ever had with a girl.

Well there was that time with Roxie but he was an unwilling recipient.

So right now Barry was very much short circuited and looking at Elsa with much adoration.

Tell her.

Barry froze. He opened his mouth but nothing came out.

Finally his brain took charge of the the situation. "Ready for some s'mores?" he asked breathlessly.

Okay it wasn't romantic but give him time. He'll figure it out.