If a creature was magically flipped inside-out, you might as well give it some kind of elastic and transparent membrane, not to be confused with skin lol, that would hold the guts together like fruit stuck inside jello.

Internal Walls

Technically speaking, surgeons do open up human bodies during surgery and you can move things around a bit. So in theory, you could say that blood would NOT be squirting out as blood travels through internal vessels, AKA like inside skin tissue. So, skin is like external walls.

Ant-Man Man

But the body also has internal walls, coverings, tissue, cell walls, etc. But to be completely literal, if you were folded inside-out, you would become like an ant as bones are at the center on the body, basically. So, you would become Ant Man. Maybe they got the idea for Ant Man from this Inside-Out Man, just kidding. At least Ant Man was kind of cool.