I have no idea why everyone is freaking out. This was unfortunate for sure, but now he (and the readers as well) have a proof that Kumika likes him back. They can (and let's face it, will) turn it around after one sincere conversation.
He didn't went overboard with his explanation of events either. This was a mistake, and it's not like he can just ruin someone else's proposal for himself (or pay back for that diamond). That's not who Chihiro is.