Show what you found out
The culmination of a successful science fair project is in the communication of the results that you have achieved. Essentially you have worked on the project for a while and now you are sharing with the world just what you managed to find out through your experiments.
This can be done through your final report, the model that you may have constructed and the display board. Now since you are considering a prize in the science fair competition you know that the judges will not have time to read your full report.
The maximum that they will read is the abstract. Make it count. What you need to do is make sure that the abstract includes an introduction, the problem statement, the procedures you used, the results you obtained and the final conclusion that you drew.
Try to keep the language simple, don’t add too many technical terms or abbreviations that people may not be familiar with. Meet the word limit and don’t add any images or tables to the abstract. That is for the pages that give details of the procedures that you followed.
If they want the judges can always flip through to the relevant page. So ensure that the entire report is well written and communicates all that you did on your science fair project.