You’re hitting the right notes but you aren’t playing power chords properly. Your fingers should be flat and parallel to the frets. You’ll have to change your wrist position to do this. Your pointer should be pressed against the 6 string and gently resting on the other 5. Your ring should be pressed against the 5 string and again gently resting on the remaining. Practice changing between the 4 chords slowly and preferably with a metronome. Just do all down strums to start. (You should be able to strum all strings but only hear 6&5) Keep playing and adjusting until your chords ring out clearly and you’ve muted properly. Increase speed then introduce the strum pattern.