Nerves, this is the problem of a small poker experience. It should pass with time, don't worry. You have to understand your system (strategy) for the tournament. How you should play, you must clearly understand your actions. Of course, it is impossible to be high in the table every time, this is a feature of poker. But after the relegation, you should not have any thoughts that you played wrong, stupid and lost. You can lose because of failure, it's okay, it's not a big deal! You should study your opponents well, determine which hands to play and how to play, and follow this strategy every tournament
Late stage you must approach, at least with the average stack of the tournament, otherwise you can not count on high places. If you have a good average stack, play correctly and the percentage of hits on the final table will grow. If you go near the end of the late stage list, it means that you are playing the middle part of the tournament incorrectly, and it is necessary to analyze and change the style of play in the middle of the tournament.