Have you read Feel the Fear? I really recommend it. If you can, get hold of a copy and read it before the meeting. It's a lovely, gentle, very clever book on how to deal with anxiety.
If you don't get hold of it, the key exercise in it is: Just imagine the worst that could happen - they sack you. You leave. Unlikely but possible. Think of different ways you can choose to handle that outcome.
You can choose to use the time to make positive changes in your life, to look for new work, or retrain, to set up a company of your own, enjoy being with your family growing up or fight for unfair dismissal. You have lots of options. you are in control of your response to worst case scenarios.
Go in assuming all will be well. Try to get there early, lock yourself in a loo and breathe deeply and slowly, saying the word 'Calm' in your head, over and over. That's a very useful trick I learned from a hypnotherapist and it works. Don't drink coffee or anything that will make you jumpy, wear soft clothes you feel comfortable and smart in, and plan something for straight after work that you really want to do, even if it's just buying cakes for tea, or going for a swim, so you have something to look forward to.