In tournaments I get the exact same score as others who make the cut off … so how come I don’t..

In tournaments it’s not just the score that decides who goes through. If players are tied, the game uses tiebreakers. Things like how many times you dropped a shot right next to the hole, or how close your shots were overall, come into play. So even if you have the same score as someone else, their tiebreaker might be better which is why they make the cut and you don’t.