Heres mine, yes It's not horizontal - but follows the line if the bodywork slightly... Whilst I'm a bit OCD it looks right to me, and if I positioned the plate horizontally then I'm introducing another angle into the whole picture - and that would trigger my OCD !
Look at the position of the parking sensor (below, left of the plate) .. I think the plate should be clear of that - but it might just be picking up the bottom left hand edge... I could of course move the plate further to the right.. But I like it where it is - and that then means the fascia behind it falls away as it rolls round the edge..
Whadya think ?