Before participating in a short contest understand that you will be competing against people who have been doing this thing for the past 3-4 years(generally, some are doing it for more than 10. Petr Mitrchev also participates sometimes in CodeChef short contest and he has been doing this for more than 15 years.)
Having said that you will always be at disadvantage as far as rating system is concerned ,if you are a beginner or maybe at an intermediate level. You can only perform good in short contest if you have a idea of almost every standard trick and algorithm out there. Because the only thing that matters in a short contest is how fast you can code up the thing with the stuff you already know.
And like every other top competitive programmer says, Upsolving is very important. So keep participating and Upsolving.
You will get better in no time.
Happy Coding and don’t care about a rating drop here and there.!