Hey Ringo,
I would recommend the following for your 3K time-trial:
1: Warm-up (10-15 minutes easy jogging)
2: Drills (high-knees, straight-legs, fast-feet… x 2)
3: Strides (3 strides, each one getting a little faster… easy jogging back inbetween)
4: Time-Trial… ALL OUT!
5: Cool-down (10-15 minutes easy jogging).
Good luck!
You may find however… you’d get a better performance (and more realistic) if you do a 5K park-run. You could swap out no. 4 above for the start of the run. Also more fun to do a 5K park-run rather than doing a 3K on your own? Then use the running calculator here to get your 3K time:
https://runsmartproject.com/calculator/