Ok, I've done it! So, how do I maintain exactly?

I reached my goal of 120 lbs on Friday (down from 160) thanks to this forum, MFP and months of hard work. The switch to 'maintain' seemed easy enough on MFP but I'm 3 days in and I've put on 2 lbs. MFP suggests 1540 calories to maintain on a sedentary level even though I walk 7 miles a day and I'm constantly on my feet. I've been eating around 800-1000 to lose weight as I'm only 5'2", but I'm not sure what my maintenance level is exactly. I'd previously guessed it was 1400 but that doesn't appear to be the case. Could my maintenance calories be around 1200? It's suddenly becoming very clear to me why I've always struggled to keep the weight off.