Nothing you write here proves this. You have made it an axiom. There is nothing logically impossible about Being being limited, implying a boundary and nothing (Nothing) outside that boundary. This may be difficult to conceive, but not impossible.

As this is a fundamental axiom of what you write, logically it is an invalid premise and, as you point out yourself, even if the reasoning is correct, being based on an invalid premise means that conclusions are not (necessarily) valid.