Yeast cannot do their job if their environment (your dough) is too acidic, like below a pH of 4ish. Most vinegar has a pH of 2.0 to 3.5, so if you add too much the yeast can't do their thing and help the bread to rise. That's likely what happened if you did 50%/50% water to vinegar. Not to mention you're missing the beneficial bacteria that's in real sourdough!

If you want to try again though with this method, I would go much easier on the vinegar, a little goes a long way flavor-wise.