Hey! Lonelybunny!
What did we talk about earlier?! 
This is a great example of us finding things to be anxious about, and using Google to try to prove and rationalise our fears.
Yes, there are stories on the Internet of people putting on lots of weight and having lots of other bad side effects on SSRIs.
But think about it. There are thousands and thousands of people taking citalopram and other ssris.
Only the people with major problems with it are posting on the Internet about it. Those with no problems (the absolute vast majority) are much too busy getting on with their new and improved lives to be posting about their great experiences with the drugs!
So, check yourself. Be aware of what it is that's your main problem with your anxiety. You managed to pick it out earlier - you always feel as though you NEED to be anxious, and look for things. Learn to accept this, rise above it and see it from the outside. The point in taking the citalopram is to slow the thoughts in your head by removing some of your anxiety, giving you the ability to rationalise your thoughts much more easily.
Does it matter if you put on a bit of weight? In the bigger scheme of things, no, not at all, as the advantage of being able to overcome your anxiety. And it is DEFINITELY worth it.
You are aware of how you can prevent this happening. There's no point in worrying about it, you just have to act on it.
Say you do put on weight (worst case scenario). You are perfectly well equipped to deal with that. You know what you need to do. Decrease portion size, be aware of snacking, exercise.
Stay strong. The light at the end of the tunnel is approaching!