I just got into the ideal weight category, up until now I'd been in the underweight. (I actually am trying to gain weight because I am way too skinny)
Don't take BMI as perfect. First of all remember that it makes no distinction between muscle and fat. And I'm not entirely convinced by where they put the barriers between ideal and overweight tbh.
If you are going to the gym daily, you are probably quite well muscled, which could be why it's saying you are overweight.
Also, you should make sure that the height you entered for yourself is 100% accurate - don't just guess, get a measuring tape







