notes sound wrong when plucking, even though the strings are in tune

i'm a new bassist and i just got an amp the other day. one thing that i've noticed about my playing is how out of tune my bass notes sound when plucking them. however, i now tested just pressing the notes onto the fretboard without actually plucking the string (to see whqt sound comes out of them), and the notes seem to be correct. so the strings are tuned correctly, but anytime i try to actually use my plucking hand to play, the notes end up sounding completely wrong. what could be the issue?