How can I fast correctly?

Our church is having a "famine" day on Saturday until 6:00. We did it a few weeks ago, and all day long I was counting down until 6:00 so I could eat. Every time I thought about food or how hungry I was, I tried to pray for starving people and thank God for my blessings. Is that what I'm supposed to do? Is it wrong to be obsessed with food while you're fasting, or is that normal?