My big concern other than crashing is air sickness.
Small wonder that it will be your first flight, then. I don't know if I can calm you down, or indeed if I even should. This kind of fear cannot really be explained away as it is not rational, it just happens to be there. Nor is it unusual, quite the contrary. You are in good company.
What I can tell you is that I have flown with many anxious passengers myself, and I think that some of those few who actually felt tummy flutter inflicted it on themselves due to their own very fear that it should happen. One piece of advice: Some people are so afraid of being sick that they do not eat before a flight, thinking that this will save them.
Beep! Wrong move!: This will nigh on ascertain that you get sick, so don't fall into that trap. Eat just as usual.
Other than that, you can try to bring an mp3 player with some soothing music or whatever helps to make you calm and maybe something to read, or a crossword. You get the idea: anything to keep you occupied (anything but booze which seems to make matters worse rather than better).
/Claes