My advice is to restart from the ABC.
Lack of concentration ? ^^
Relax yourself with your method.(this is the most important)
At candle or lamp light or reduce the lighting in your room.
ABC visualization.First start with a small object with a simple shape(squares circles, triangles with monocromatic color look it look it shape it color touch it when you are sure you get it's image and shape, close your eyes and visualize it in your mind icrease and decrease it size.
3D Objects of the same color.Pens, Pencils,computer mouse,small books,Post-it
After start to change the color of that abject rotate it change it shape let your subconscius restart to work.
4D objects (the shadow included) :)Change the color of the shadow.
The most most important is :ENJOY what you are doing.
This will fix your joy emotions in your mind.
If you feel it is boring stop and restart in another time.
Me too i've got the same difficulties but i practice rituals every days :)