How to approach girl/fix this situation?

I've been going to this clinic and there's this cute girl working as a receptionist there (R1). She's really nice, always making small talk with me, very hospitable, giving me water when she noticed I was parched, and always looking and smiling at me while I'm sitting in the waiting room. But a couple days ago, she made a mistake on my invoice and I went to the clinic to get it fixed and there was another receptionist working at the time (R2) and I was explaining back and forth about what was wrong as R2 did not understand and then R1 walked in and I called her out on making the mistake, not in a mean way, but I guess it wasn't too nice either because she looked really sad after I did that and I feel soooooo bad right now. I was actually gonna ask her out that day, but I'm worried I may have put myself in a bad light now. What can I do to try to fix things and hopefully ask her out successfully?