Make yourself think about other possible approaches. Build in adjustments. Build such things as belt tensioning pulleys, slotted screw holes for adjustment, flexible couplings, etc. Remember that dimensions and lengths can change with temperature, moisture, time, etc. Once you have a working device your next assignment is to find out what makes it NOT work.
Reliability here is the name of the game, and it only comes about from testing and modifying.
If your device does not work without tender care and careful adjustment it probably will not work at the contest. In these contests a reliable device which operates at moderate speed almost always beats a semi-reliable device which is blazingly fast. Turn your development device into a finished product. At this time you should clean up wiring and other loose ends. Remember that your colleagues and possible future employers will be looking at your device and forming an opinion of you from what they see.