Well the first thing a professional does is a literature search. Have you done any research on the physics of vibrating strings? If so be sure to properly site your sources in your paper.
As is typical in such settings there will be an simple idealized case and then there are deviation from and corrections to the simple ideal which typically you can write PhD theses on if you go far enough.
So explain the physics including simplifying assumptions. Compare the experimental results being careful to both show correspondence and point out discrepancies. Then as you have time and inclination you should elaborate on the discrepancies, how much is attributable to recording error and experimental error. What models exist which deviate from the simple ideal which could explain discrepancies. Ultimately the best science report should end with suggestions for further experiments to clarify or illuminate these points which are raised.
You do not have to reinvent the wheel so its OK to blatantly copy and refer to other people's ideas on the behavior of vibrating strings or on the experiments which observe them.
It if of course VERY NOT OK to fail reference those other people and leave the impression (even if accidentally) that those ideas are your own. But I think you'll find with a few google searches and a trip or two to the library that you'll have a hard time keeping it short, rather than at having enough to say.