Jamie, wouldn't that be a push pull rather than push push

Oh no that might confuse poor Andy even more

I'll shut up.
Andy this is getting silly now, your panicking too much. get it roughly between 5 and 7mm and you will be good to go.
For any catastrophic failure you would have to be seriously loose and by that I mean the chain flopping around all over the place. At worst it could go one of two ways but NOT likely with the method of installation your using by removing the cam cover and measuring with a ruler
At worst the chain would be so tight you end up with starting problems/screeching in which case you gonna sh1t yourself and not go any further. This is NOT going to happen using this method of installation. And second, it could end up too loose where you hear a little bit too much rattly chain with the engine fully warmed up. Yet again this is NOT going to happen using this method of installation. Either way if by some stupidity one of these two things occurred, it's nothing that can't be resolved quickly with a slight tweak which can be done without removing the cam cover and everything else again.......so stop panicking. It's no different from measuring the slack in your drive chain.
My next guide will be titled 101 ways to measure a chain
PS take the "I tried" out of your thread title as it puts negativity in the way before you've even started. Chin up and remain positive.
(:-})