Proffesional comment? ... i dont know?. I`m not proffesional, only learning. OK! I like your masks, looks great, but for a good Book cover it doesn`t look well done.
First, Motion Blurr in your Background doesn`t fit there great. Try some business texture, like papers, folders or something like that on the back with lower opacity or with same masks... use some Color Burn or multiply for texture, or even use some of the default filters such as Extrude, or mosaic or glass and than Motion Blurr it.
Second, under left top corner, the white and the blue colors aren`t matching with colors under right corner...
Just keep creating new ideas for this cover and you definetely will came with something even Better [righton]
Good Luck