Do your best! Keep to your plan but don't get discouraged if you have an off moment or day. Adding strength training will definitely help. Do you have other dresses that you could wear just in case you don't make your goal? Actually, you have 2 sizes in there that you could make your goal... if you exercise and are on plan re:food, why don't you make it a reward to get yourself a new dress that showcases that loss?
That way, if you fit into the sz 12, awesome! If not, you still get to feel good about your loss.