I'm going to offer something to someone after they've already declined it.
Why would you offer it to them a second time?
I wasn't sure if the person wanted it, so I'll offer it again.
It's good to clarify whether or not someone wants something, but once they decline it it's a good idea to stop bothering them. If you offer someone some thing after they've already declined, they are likely to be annoyed and they may avoid you.
I just wanted to not come off like a douche bag.
That is understandable. If people decline you should learn to respect it and try not to be pushy in the future.