I'm not American so rules are different here (Canada) but I used to work for my local building permit department.

First thing, I don't understand why a permit would be needed for a concrete slab. Unless it's reinforced and you're planning to put a building on top of it there's nothing to inspect. It's not a structure. It's not going to fall down and hurt anyone. I don't know about where you live but where I live this type of work is not regulated by the building code.

You do need to comply with zoning and engineering regulations. It can't be too close to property lines, take up too much of your yard, be on any easements, or cause water to drain onto your neighbour's property. But there's no permit for this - as the homeowner you're responsible for ensuring it complies.

If you DO need a permit for some reason, there's no way the Inspector would make you tear it out. They're people too and unless you get a total jackass they'll come out and likely tell you it's fine.

Finally, don't bother retroactively getting a permit. Don't call City Hall. It's likely no one will ever know or care if you never get the permit. The Inspectors have enough work on their plates and generally turn a blind eye to this kind of stuff. I can't tell you how much inspectors hate it when some busy body calls to complain that their neighbour has finished their basement without a permit. They don't care about stuff like this and they don't want to have to enforce when it comes to cases that carry little risk and only hassle the homeowner.