If the filling is too thin, it could be due to excessive liquid from the strawberries, cream cheese being too soft, or whipping cream not whipped until stiff peaks. To rectify it make sure you are following the instructions well like draining the strawberry puree or checking the consistency of cream cheese. The other option would be to refrigerate the filling for 5 to 10 mins and try but do not refrigerate for longer if intending to use as frosting as it might change the texture.