Q: AC not cold

Ever since I got my Jeep, the AC is not as cold as other cars I ride in. I usually never minded because I enjoyed having the windows down, but now that I graduated college and have a job I figured it's time I spend some money trying to fix it. I bought an Arctic Freeze AC bottle that has a gauge on it and watched videos on how to recharge the AC. When the compressor turned off, the pressure gauge had the needle going to the top of the green, or filled, section. When the compressor was on the needle went down to the bottom of the green section or top of the white, underfilled, section. Since the needle never really left the green section I am wondering if the AC pressure is fine and it is just a low quality AC, or if I am reading the pressure gauge wrong and still need to recharge the AC. Any help would be greatly appreciated. Thank you!

My car has 151000 miles.
My car has an automatic transmission.