As has been said to you...recently in fact...it takes time to become a good racer. It took me several years before I was in the top 10 at the finish of cat3 and vets races...a few more years before I won my first race.
Think about what went right and what went wrong in today's race.
Do you keep a journal? You should. I have 20 years worth of the darn things. Very valuable...Write down what went right and wrong, how you felt, etc.
Then think about your preparations. Do you lack strength and conditioning? That takes time. Did you make mental mistakes, inadequate food/water, etc. It is not one thing but many that go into making a good racer.
Give it time and don't give up...