How to gain height at age21 .... i only want 3 inches more ... is there any options for me??

Accept it: I am sorry to tell you that most men stop growing by age 18 (though occasionally there will be slight increases up to about 21). But no 21 year old is going to grow 3 more inches. Once the growth plates of your bones have closed further growth is impossible. At this point all you can do is accept that this is who you are and how tall you will be.