Practicing the piano is like anything else you might want to do: if you want good results, you have to do it right. Let’s compare piano with running:

I had a couple of students in the past who tended to miss notes here and there during music reading. This isn’t an unusual situation since there’s so much going on when someone is reading music. A few things can improve the situation if you’re one of those players who seems to overlook music notes.
An effective way to memorize and understand primary chords for each major scale is to write them out for yourself. You might even consider writing out EVERY chord for all the major scales. This exercise will help you internalize every chord associated with each major scale.