(Here you describe the key issues and constraints of the project, as well as the criteria for the success of the project).
(These issues would be all the problems you encountered and how you resolved them).
You are not expected to have everything working perfectly first off.
(In fact for the HSC the more problems you have and resolve, the higher the marks received, as the student/s were more challenged and had to work out solutions).
Where you made some code errors and the Scratch did not work, as it should have. There could have been problems with the computer graphics card, which changed the way the Scratch behaved.
Rubber Band Racer
With the rbr there could have been problems with the assembling and gluing. Maybe the rubber band slipped and the racer stopped.