You should be able to cut 5 lbs easily. Put on the old school-plastic bags or buy a sauna suit and just jog lightly in a warm room for about 30 mins with the suit on and then hit the sauna for another 30mins. You should be fine then. Once you make weight, you have till later in the day to hydrate yourself. That's what you have to do.
BTW, what state are you boxing in? In Florida, you can't weigh in over weight. If you do, you have two hours to make weight. But in New York, you do have 3lbs in the prelims but have to make weight by finals...if you make finals. So if you're boxing at 147lbs, you can weigh 3lbs over which would be 147lbs+3lbs= 150lbs for the prelims but will eventually have to make weight if I'm not mistaken