请教这个句子里 if 的用法
And it's not just for senior prom,it's for a senior project!If not Project Runway..All of it added up to a passing grade and a one-of-a-kind,if not comfortable-kind,of couture.这两句中的用法和意思我不是太明白,主要是不太明白这两个if的意思 ,希望英语达人们能帮忙解释一下这两句里的if的用法和 整体的意思,
原文如下：And it's not just for senior prom,it's for a senior project!If not Project Runway.The ingredients:117 packets of juice!One boyfriend to help drink all that juice.Some thread,some hot glue,three weeks to assemble.All of it added up to a passing grade and a one-of-a-kind,if not comfortable-kind,of couture.