Here is the original item:
If his friends walked into the bookstore
(A) Boris
had a stack of car magazines as camouflage,
(B) but he
was really reading Better Homes and Gardens, studying decorating
ideas (C)
to spruce up his first apartment.
You wanted to do this:
If his friends walked into the bookstore Boris had a stack of car magazines
as camouflage, but he was really reading
Better Homes and Gardens, studying decorating
ideas,
to spruce up his first apartment.
Adding a comma after ideas creates a problem. To spruce up his first apartment is an infinitive phrase. When a phrase of this type concludes a sentence, you do not need a comma to attach it.
You might want to review the rules.