I would suggest a 600m time trial after an abbreviated workout to tune up for the 800m. Maybe you've done something similar already, but the 800m can be shock to the system if you just go out and do it with no prior 800m-specific work.
EDITED to add. I'm not saying you'll get hurt. I'm saying that you'll do better if you do some 800m-pace intervals in the week or two leading up to the time trial.