Hey Sapphie,
Bike riding is EXCELLENT! Last summer, when i had time, i would go on a strong, 1hour bike ride around my city. Mine, like yours, has no hills. Within 1 week i had already lost 7lbs. Keep at it, also, to help maintain a healthy diet, i would add fiber tablets. They absorb water in your stomach and it makes u full, and it collects unwanted waste in your body. Good luck