Hey there. You're only sixteen. You are perfectly normal. As you get older you will gain the confidence and maturity to handle these feelings. It's natural. Don't worry so much. Enjoy fantasizing about these girls and keep trying... you'll get there sooner than you think!
Before you know it you will be much more comfortable with your sexuality and women. This is just one of the normal stages of growing into a man. You're fine. Accept yourself and your feelings and enjoy the healthy process of sexually and emotionally evolving.
Lucky you, it's all in front of you.