Congrats on your upcoming graduation!
Unfortunately, event-based weight loss goals are rarely successful. Your best bet is to set a good 2lb/week weight loss goal between now and then (which is safe for your size based on your ticker) and aim to be as healthy as you can. Understand that you won't lose half your body weight by then, but you can look and feel so much better.
Start tracking your nutrition; knowing what you're eating and when is the most powerful tool you have, and all the exercise in the world won't help you if you aren't eating a balanced, reasonable diet with restricted calorie intake.
You can do this!