You didn’t say what your reasoning was, so I made a stab in the dark. I don’t agree with your reasoning though. My issue is that there are a number of logical traps in words like thing, nothing, being, existing.
For instance, nothing is no-thing, the absence of a thing. But only things can exist, so it makes no sense to talk of no-thing having existence. But if no-thing cannot exist, does that mean something must exist, in other words must there be something rather than nothing? Some people do make that argument, but is it really logical or just a play on words?
Then, if a no-thing cannot have existence and only a thing can, does it make sense to talk about non-existing things, aren’t they instead no-things? And so on. To me it seems only to be playing with language.
Even then, if we were to put all that aside and for a moment accept the notion of a necessarily existing being, surely that means that every aspect of that being must also necessarily exist, since otherwise, if it had optional properties, it wouldn’t exist necessarily, it could have been different. But if logic dictates that it couldn’t be different, wouldn’t logic then be more fundamental than God?