Part 3 will be 8 questions about NFRs - and how your design addresses that - for ex., how does your design handle scalability.
so,
you should look to take part 3 as soon as you finish part 2 - this will help you to remember your design and refer the classes in your answers to part 3.
part 3 is also for another thing - to find out if you were really the guy/gal who did the design. so, you would be expected to know & defend your design...