I think the balloon analogy does not work well here. As far as we know the big bang was the start of our universes spacetime. There are plenty of theories on what might have happened “before.”.

Here is a good playlist to get you started on learning some more info.

youtube.com/playlist?list=PLsPUh22kYmNAV2T4af0Di7…

And this video from that playlist is directly related to this discussion.

youtu.be/K8gV05nS7mc