Why is my cat too scared to go outside unless im with her?

I adopted her when she was about 8 or 10 weeks old from an animal shelter and she is now a year old. I've been allowing her to go outside since I got her, however when she does go into the backyard its only about 10 feet from the door and no farther. Very rarely I see her sneak into the neighbors yard but she stays right by the gate and comes back when I call her. I leave my backdoor open in the mornings and she will just sit on the doorstep but won't go out unless I go with her, and even then she stays close to the door. if I close the door and she is outside she scratches the door and cries until I let her in (I never lock her out, it just happens by accident sometimes). I just find it strange because we always had lots of cats and my mom always took in strays when we were little and all of them would go outside for hours at a time. Does your cat do this? And please don't tell me not to let my cat outside. Thanks.