Oh, I'm terribly sorry.

Literal

Oh, apology-not-exist [humble-ございません].

申し訳ございません is the humble-register apology: 申し訳 ('excuse') + ございません (the keigo negative of ある). Stronger and more formal than 申し訳ない or ごめんなさい. Used by service workers, in business contexts, or when apologizing for a serious mistake. あら is a soft feminine interjection of mild surprise or dismay.