Your feeling that you could/should have done more/better in your doctoral studies is, of course, completely valid and completely misguided, as it is true for just about everyone. Of course, you could/would have done more if you hadn't started the process as a novice, but rather as an experienced researcher.
You have a different perspective now, since you have gone through an extensive learning process and have gained skills that you didn't have a few years ago. That affects your judgement about what you are capable of. Yes, you are capable of quite a lot more now, but it is a mistake (logical, psychological,...) to project that back five years.
Your sense of "failure" would really only be valid if you now have the same naive views that you had five years ago. But if that were the case, you would actually be an imposter, but wouldn't have any way to recognize it.
This is classic imposter syndrome and many people at your stage suffer from it for exactly these reasons.
However, let me try to give some guidance on your question. First realize that the range of positions as an "academic" is very broad. Some of us are primarily teachers. Some primarily researchers with only a bit of teaching - mostly of very advanced students. There is a fairly smooth gradation between those extremes. So, first look at what sort of position you would like to hold. Then explore what such people do and what is considered valuable for such a position.
With that background, work to fill in your CV (and your experiences) that give you the expertise to do those things. If you want to be a researcher (my assumption, since you list post-doc as a tag) then you should work on getting things into the publication stream and also in building collaborative arrangements with other researchers in your field. Your advisor(s) can probably help you get "connected" to the wider research community as can attendance at conferences - especially as a presenter. But you can also get connected to other researchers just by serving on conference committees in some fields.
But "academic" is probably too broad a goal. Narrow it and then work to fit that narrower definition.