What you are doing is wrong and prohibited. Once you begin the prayer, you must finish it regardless of the small mistakes you do.

My mistake in salah is my pronunciation, and absentmindedness. It happens so regularly, I just get angry at myself that I can’t perform prayer like everyone else, and fear it won’t be accepted, so I repeat it and then end up doing the same thing. Also during the third Rakah for Maghrib if I read Surah Al Fatiha and then say Basmala, does this invalidate my salah?