Cant calculate my calories, help?

So hi I'm on a 1200 calorie diet I'm 5'2, about 120 lbs and I'm 16 I'm trying to lose a little fat so you can see my abs, I'm currently at about 20.6% body fat I'm a female btw. So my problem is that altthough I eat very heatlhy sometimes I can't calculate my calories right and uncunsiously go about 50 to 100 calories over the limit, I want to know does that affect my progress a lot or what? Btw any tips on losing fat quicker? I do interval training three times a week for thrirty to forty minutes and two days of regular cardio or bycicle and I lift very heavy weights, I eat tuna, grilled or boiled chicken, legumes and vegetables, low fat yogurt, casein protein basically healthy so any advice? Also how long should it take to see results I work out five times a week