What's a good weight for me?

Asked by Zeta41 (5) December 1st, 2013 from iPhone

I’m a 5’3” 15 year old female. I currently weigh 141.5 pounds, I was 162 pounds a few months ago. I checked a BMI scale, and it said that I should be 120–125 pounds for my height and age. My bust is rather large for my age, so I don’t know if that gives or takes away from my weight, and since i’ve started exercising daily, i’ve gained alot of muscle in my arms and especially my legs. My deltoids,triceps,quads and calves are quite developed. Now, I can’t seem to lose anymore weight, i’m stuck in the 40’s. I still exercise daily, but i seem to only gain…muscle? I don’t think i’ll make it to 120 or even the 30’s… Is that bad? Am i doing something wrong?