Comparing nets to matches is like comparing apples to rubber ducks.
The bowling machine is not trying to get you out, the artificial surface is even, and the bounce is uniform. No one there to catch you neither. Furthermore you know exactly where and when the ball is released because it is a machine, and the batsman is under no pressure. You don't have to take confidence into account.
The bowler is trying to take wickets, the pitch is varied, and the bounce can be uneven. Your batsman is low skilled and you are under pressure. Also due to the bowler's run-up you have to manually determine the release point of the ball, so there can be more error. Your batsman is fresh and confidence needs to build. You need to play yourself in and accept that due to your batsman's low skill level that high scores will be unrealistic for you until you can play each delivery correctly each time.