Having troubke eating enough

Hello, I started the FB meal plan a few days ago and I'm following the 1600 cal option and I find so far it is too much food for me. It says to listen to your body, but in the guide also says you should not go below 1600 cals. Some background: before starting this I didn't eat horribly, but only 2-3 times a day, and probably not well balanced but I have never had an issue with under-eating. I'm 5'0, about a size 8-10 and want to lose 20-30lbs (I don't weigh myself so its just an estimate). Is this just a problem of adjusting to the frequent eating, or is it ok if im below 1600 since I'm so short? Or should I just try harder and eat when I'm full? Thanks for any advice!