Yes, the CG is measured from the leading edge.
If you used 0.4 mm width, it is no wonder that your wing is much lighter.
It is OK if the upper surface keeps in shape - and does not start to flatter when flying.
Because if you print thinner as 0.5mm, the perimeter of the upper side will not merge with the perimeter of the inner spars.
You printed with 0.18 layer hight. How many bottom and top layer you used?
You must reach 0.6 mm solid for bottom and top. Otherwise the inner spars will not connect the top and the bottom layer. There will be a gap inbetween.
I like the colors you choose for the wing, it looks like a bumble bee.
Speedy "Bumble Bee".
And thank you for the label with "By Wersy" :-)