There are a couple of ideas that come to mind.
Maybe it would be better to use the word '약속' and say '오늘 약속 없으면...'
I think it would be more common to phrase a sentence like this as in '같이' rather than distinguishing between 'you' and 'I'.
Then, I wonder if it would be better to use a suggestion format like '할 까?'
So, assuming that this is a close friend and a 나이 친구 I was thinking:
'오늘 약속이 없으면 우리 같이 퇴근 할 까?'