You're not alone! It's hard, even when you KNOW that it's healthy to gain some weight.
I'm at 27 weeks and have managed to keep my weight gain to about 13 pounds so far. That said, my doc's visit yesterday was the first where I saw a big jump-- 5 pounds in a month. It was hard. I'm also looming up on 250, which is another mental block. I started at 322, so I KNOW I'm still WAY thinner than I was.
For me, it helped to continue to plan meals and menus and workout as my body allows (starting to run into limitations there.) I don't obsessively count calories, though I check periodically to see that I'm not WAY off base.
I've stuck to a moderately bandster friendly diet and have intentionally enjoyed some non-bandster favorites that don't work when my band is tight. HOWEVER, I'm eating more things like big leafy salads (light on the dressing) and raw veggies that I have trouble with otherwise. I'm enjoying a few more whole grain breads and other HEALTHY options that would otherwise give me trouble. My latest obsession is a broccoli coleslaw recipe from an online blog--I eat it by the bowl, sometimes as lunch itself. By enjoying the healthy stuff that doesn't work with the band, I feel like I'm getting a treat in exchange for the weight gain. The sugary/fatty stuff doesn't make me feel good, so I avoid it.
It's hard. And depressing. And crazy-making. You're not at ALL unreasonable for finding the prospect of weight gain terrifying. But you DID THE RIGHT THING by getting the unfill! Don't forget that a good 20-25 pounds of pregnancy weight gain is baby-related, NOT counting maternal fat gain! That doesn't mean you'll be 20 pounds lighter the day after babe is born, but you'll be on your way. AND you have your band. It WILL work after baby is here!
Good luck to you. There are lots of successful bandsters who have had babies, lost the weight, and gone on to reach goals. You can be one too!