Hello Stephen,
I am sorry to hear that. You have bought AVG PC TuneUp license for 3 PC's and it is valid until 4/16/2019.
Please refer this article http://support.avg.com/SupportArticleView?urlname=Activate-AVG-PC-TuneUp to activate the program with the license number. If you face any difficulties, provide the screenshot [http://support.avg.com/SupportArticleView?urlname=How-to-create-a-screenshot] of AVG PC TuneUp interface to check and assist further.