sentance

I would use either:

However as I stood to go, I heard the words, "sorry for keeping you waiting."

or (if you want to emphasise the word "sorry"):

However as I stood to go, I heard the words, "'sorry' for keeping you waiting."

That's, of course American English. British English might be more like:

However as I stood to go, I heard the words, '"sorry" for keeping you waiting'.

Reverse the double and single quotation marks and put the period outside the quotes, I think, for British.

In critiquing mode (sorry, I can't help myself), I would rewrite this:

As I stood to go I heard, "sorry for keeping you waiting." (You might really need "However," depending on the context, but probably not. It's a slow word.)