There are worse things you could have done, take it that way. You had an arguement, things were said that weren't meant, pretty sure that's how the majority of them go! If you really are worried she took it to heart and its going to permanently scar the relationship, then take her aside today and, instead of bringing up what happened and how much you regret it, why not instead show her how much you love her? Give her some flowers. Make it positive, heart-felt statement. I think saying "I love you like no other and I'm so glad I have you" means more than "I'm sorry" in this case. Of anything that girl needs to hear right now it's that, not being reminded what made her cry in the first place!