How concerned should I be?

I see i don't have authority to post attachments or i would include picks. My 9x18 intex, in third year, is leaning very slightly to one corner. From a horizontal photo it seems like it dips there about 1-2 inches. The Boards i had under two braces have popped up. I'm guessing i didn't have them centred properly, as i set this up myself (thanks to selfish teenager refusing to help) on a crazy hot day and clearly rushed things.

How bad does the lean have to be for it to risk collapsing and flooding not only my back yard but my neighbour's, who is a bit downhill from me so they'd get the worst of it? Do i need to drain and start again? I've already decided to ban horseplay of any sort in the pool this summer.

I don't think you will have a problem, soft sided pools are made so that they can be put up on a lawn that is not perfectly level and then taken down again later if you want to. My advice would be watch it, if it is getting progressively worse than you could fix it.