How to Apply Hydroquinone 4% if There Are Too Many Dark Spots for Spot Treatment? Its Too Time Consuming

My dr gave me Hydroquinone4% & Tretinoin. its difficult to use because the marks on my back go from one side to my shoulders to the other (just the top part of my back) &my dr told me i had to spot treatment this 2 a day which is impossible to do because its so many.I just started having my mom put it on my back hoping later on it wont fade the surrounding skin. What should i do to make it easier? is it ok to spread it on the infected areas instead of spot treatment?