So have another referendum on the subject every year until there's a decisive outcome. Maybe pair it up with local council elections to save money. Sounds OK to me.
It was decisive. There was a clear majority, albeit a slim one. But still a majority. Not like there were 2 votes in it. Difference of more than a million.
If you start trying to define majority as anything other than side A got more votes than side B, you're trying to rig the system to get the result you want.
You can argue ~28% didn't vote, but they had their chance and couldn't be arsed. Maybe they didn't care, maybe they have become disillusioned with politics and thought "what's the point".
Don't see how your suggestion fixes that, other than watch the turnout get lower and lower each time as more and more people become disillusioned by the whole process, because nothing changes.
Our democracy is already a thin veneer... this will only make it worse.