Record all your questions and observations in a bound notebook. Don't erase, just cross out errors. Write enough so someone else could reproduce your experiments. Diagrams can save lots of words and help make your ideas clear. If you make measurements, record your data, with units.
Tables are useful for repeated similar measurements.
To make the logic of any calcuations clear, first record the formula you used, then show the numbers used to evaluate the formula, and finally your answer. With all this thought and record keeping, a final report to your class will be quite easy to put together.