You can see multiple flaws in the argument from contingency please share one or two.
Most of them have already been mentioned. It's full of blind speculation. Just for starters and even without thinking much about it... Point 1, we don't actually know that anything could have not existed. Point 2 is an intuitive speculation based on our experience within space-time, and there is no particular reason to think it can apply to reality itself. Point 7, the whole idea of something that cannot fail to exist is problematic. What could possibly exist whose non-existence would cause a contradiction or otherwise be impossible? Point 8 is contradicted by the space-time manifold as I've already explained multiple times.
There is no strong argument to settle for the universe ''just is'' . A position which is indistinguishable from having no sufficient reason.
It's
exactly as strong (or weak) and has
just as much (or little) 'sufficient reason' as anything external to the universe that you want to make up that 'just is'. That is, unless and until you can explain
exactly how something can be its own reason to exist and how its non-existence would be impossible.
Added: And, of course, even if we were tempted to accept the entire argument, it isn't an argument for a god - just for some undefined 'something' that couldn't fail to exist...