If you've promised something, once you've said it you have to do it.
Tips
usage
At the start of a sentence 说到 means 'speaking of, when it comes to', a smooth way to change topic: 说到这儿 'speaking of which'. 提到 is the near-synonym; 提及 and 谈及 are the formal written forms.
memory
说 'to say' + 到 'to reach': speech that reaches something. That is also why 说到做到 means 'what you say, you do'.
