After 3 years lab work (including 2 changes of supervisors - change of institution as one boss left and took me with him but I remained registered with the original uni) and 6 months of write up. I am absolutely terrified of my viva!

I just keep coming up with horror scenarious in my head which isnt helping. The proposed date is the 10th June (my external could only do 3 days in the next 3 months!!). Apart from keeping uptodate with the literature and making sure I know my thesis inside out - what can I do? Im really worried im going to fail - even though I know my supervisors would not let me submit unless i was going to pass