I was sitting there looking for that grey block for a long time in your edit, thinking... no, I can't need a calibration, it always seems fine! Only to finally find out the grey block was in his original picture.
Also, fully agree, this could really need some cleaning up, there really isn't a need for all those scribbles. Also, while the orange fits the reference well, it stands out a lot against the red. This needs to be addressed with dithering and perhaps some AAing, either way, it needs to blend smoothly, to eliminate the whole sketchy feel. I also think the shadow from the leaf stands out way too much against the apple, maybe use the darkest shade from the shading of the apple and blend it a little more with AA. I also think you should fix up the leaf some, those darkest greens really stand out a lot and look more like stray pixels. Just the whole thing needs to be cleaned up.