What a wonderful tutorial!  This painting is an 8x6 on Arches cold press.
I went off rails early in the painting…my background got way too dark. I attempted to improve it by adding the bokeh effect. I think it worked out ok. 
Then the real trouble started. I removed the mask to start the petals and accidentally removed the mask off of the stamen as well. Easy fix, I reapplied the mask. As I waited for the mask to dry I thought I would do some erasing.  And then I brushed away the eraser crumbs with a brush … right through the mask and all over my lily! Oh dear! What a mess. I did persevere to finish the painting. I could continue and make further improvements but I’ve decided to leave it here and try again.