Always best to put accurate measurements and if you get someone complaining they're not as described, get the item back for a refund unless you can show absolutely that it is buyer error or remorse.   Also, whilst that neg and probably the related low stars have not been a disaster as such, your seller ratings are slipping and combined, that will cause you a problem before too long.

The measurements were accurate as far as the OP was concerned and included in their description, including the phrase "All measurements are approximate". That should give the buyer a good guide as to what they are buying surely? 

I didn't realise stars between 4.8 - 5.00 were considered low...