Let your boy be himself and if that means playing with girls that's okay. He may even have a crush on one or more of those girls. I know I liked boys in kindergarten and so did all of my girls. My 5 year old girl loves to play with boys. She connected with one boy at school and when I asked his mother if we could schedule a play date, she said no because he needs to have more boy friends. I was offended by this. Her boy was very boyish. Kids connect with different kids and sometimes it has nothing to do with if they are male of female. Try not to worry. Kids grow up and change a lot. You will see many changes before he is all grown up.
I have 8 close friends, 7 of them are male. I am a female. I connect better with men.
My son plays mostly with girls. Gilrs are better in pretend play and are more predictable. Especially if he is sensitive, he may still like to pretend he is a power-ranger, but become a little anxious when other boys play "rough".
Worrying about feelings is not a girlish behavior, it is a good trait in children since it helps them to learn - greatly. I wish my son worried about others' feelings more:)
Please do not be such a weirdo yourself and let him play with whoever he chooses to.