Yes, if you make a mistake, you could easily overdose, hypoglycemia and die. Or underdose, and become hyperglycemic and enter an altered mental state where you'd be unable to function normally, or lose connection with reality.

I don't think it's reasonable to expect everyone who takes or buys it, to be able to determine if what they need to inject into their body to survive is safe and functional. So yeah, I do think there should be laws and limits on what qualifies, and who's allowed to make it.

Do I think a large corporation is the only thing able to do that? No, but I suspect that it'd be hard to prove you can make the minimum guarantees that it's safe from the first dose to the last. And that you have resources to attempt to compensate anyone you hurt if you do break those guarantees.