Hello guys i just unboxed my dji phantom 3 standard.  I take off the copter upto 69ft. And then RTH mode get activated.  I tried to fly at many different locations in farming fields.  But i can travel upto 100ft and 69ft high and above that RTH mode activates.  Please help me to solve this issue

69 feet, that's not very far mate

Have you got the aircraft in 'Beginner' mode?