Chris, there is a picture of one of the Eoropean bikers who has hit the back of a car and literally smashed that whole corner off the tank. I would conservatively recon that the material in that area is a good 4mm at least. Also in the moulding process that corner will have more material in any case.
Put some filler on for your own peace of mind but personally I think you will be OK.
We can all keep an eye open for a spare, you never know my first bikes' tank might comeup!
I'll have a search later and see if I can find the picture to set your mind at ease.
Hope your bruising is easing. Stay safe