To lose weight and keep it off you need to be constantly monitoring your calorie intake and your exercise. As you lose weight, you will need to eat less calories and exercise more to avoid your weight plateauing (staying the same).
Also, if you lose weight too fast, it will come back just as fast and you'll end up weighing more. There are many forums here that can help you stay on track and offer you dieting advice if you choose to start/continue one.
You'll be fine