8th Grade Graduation Next Week?!?

Okay, so one week from Friday is my 8th grade graduation! I'm so excited! I bought this dress, and It fits, but I think it's look better if i lost a few lbs before. ( I'm 5 foot 4 and 138 lbs) If I eat 2 egg whites with swiss, OR a Dannon Light and Fit yogurt for breakfast, A salad OR turkey and cheddar sandwich on 100 cal bread, an apple, and a salad or something really healthy for dinner, will i lose any weight? I eat good as it is, but I like to snack, so I'm going to cut that out too. And I'm going to work out a half hour each night. Will I look any different after a week? If not I guess I'll just feel more confident! Also, I'm going to try not to drink diet coke (I have diabetes) because I heard splenda makes you hold onto fat, even though its low-cal. I'll drink a lot of water! Any suggestions on losing the few lbs! ( I wanna tone up my legs, lower tummy, and shoulders)