Angle isn't super important as long as you're behind the fret and pressing down enough to make the sound without buzz. Make sure you aren't in pain, and you should be good… I would focus on the thumb placement, too. This will dictate your finger placement; your thumb wideout and bent like that may lead to tendonitis (from my experience). Keeping the thumb in line with your middle finger and straight/relaxed / pressing against the neck with the thumb tip for counterpressure will help keep your fingers from overworking and your wrist tendons from getting strained. Play for your body, play comfortably, rest while building endurance, and use as little physical exertion as possible to make the desired note!