Is it ok for a 14 year old girl to think she really likes an 11 year old boy?

Well there is no harm in fantasy as its all in the mind. Whatever you do though don't act out those fantasies in real life as you will get into deep trouble because you would be found out. It would be best for you to keep it to yourself and stick to your fantasies. If you need sexual satisfaction then there is nothing wrong in masturbation in the privacy of your own room. Again it is private so you should keep it to yourself.