Same thing happened to me. Basically you will have to take it off and redo it. This time with wider tape. Mine surprisingly pulled off pretty easy. Cleaning the tape off the spoiler mind you was a P.I.T.A.
3M tape used for structural purposes should be installed with 3M Adhesion Promoter. You get it at you local Auto Supply Store - the one tat supplies Auto Body Shops - or off Amazon.Any advice on how to remedy this?