The measurement you get by extending your hands out is a ballpark estimate. It may not be your actual draw length. Your actual draw length is the distance from the valley of the nock to the back of the bow, when you have drawn and anchored at full draw. It does not change with bow poundage. The only thing that changes with bow poundage is your ability to pull the bow back. At a certain poundage, you may not be able to draw the bow all the way to your draw length, which means that bow is too heavy for you. It may be that you can get stronger and eventually pull that bow, or you may learn to pull more with your back muscles and be able to pull that bow to your actual draw length, but you can't do it right now and you risk injuring yourself if you force yourself to do it.
First, you should learn to draw with your back muscles. Then, if you want to draw a heavier bow, you should either overdraw a bow you can handle, as Tony suggested, or draw and hold a bow you can handle for an extended time, as I do. Trying to draw a bow too heavy for you with your arm muscles is an invitation to injury.
Once you learn how to draw a bow properly, and have a bow you can draw and anchor at your draw length, then you can experiment with differences in the way you draw the bow that might change your draw length. Rod Jenkins is famous for his classes, where he teaches people to expand more than they were doing before the class, and maybe add 1/2” to their draw length. This of course adds power to their shot. Standing upright perpendicular to the target, as Stumpkiller suggests, might add 1/2” to your draw length, if you weren't already doing that. Some people do the opposite: they choose to stand with a more open stance and shorten their draw length by 1/2” because they feel they are more accurate with an open stance and a shorter draw length. These are all tweaks you can do to fine tune your shot after you have the basic form down.