There is nothing wrong with finding a girl or a boy attractive, its how you deal with it. If this girl is appearing nightly in your imagination, when the door is closed and there is no one around. Then its not a good thing.
When you lust after someone you are not respecting them as a person, you just want their body. How would you feel if you knew that one of your friends thought this way about your sister or even your mum?
You are not a terrible human being! Don’t be so hard on yourself! Secular society is obsessed with sex and not with love. If you really like this girl then your feelings will change to wanting to care for her, respect her options and attraction. Rather than just raging hormones.
As others have said pray. If you start to have lust full thoughts go do something else. Like sport or helping out round the house. When you go to bed make sure that you are tired and maybe listen to an audio book or even the radio to help keep your mind off the subject.
It will pass.