Whether you use a jar of prepared marinara or make your sauce from scratch with canned plum tomatoes, there is always going to be a little bit of jammy, red residue in the bottom an on the sides of the container, whether that container be plastic, glass, or aluminium.
Anyone who has ever made a tomato-based pasta sauce has probably noticed the thick, dark red trail the sauce leaves behind on the walls of the pot as it is reduced. This sticky residue is (free! bonus!) tomato paste, and it should not be abandoned under any circumstances.
Don’t be lazy with your pasta-making skills. It’s one of the best comfort foods and deserves to be made with all the love and care you can give.