I did that A LONG time ago. Definately do the extra credit, I found it really easy. Don't make it too hard on yourself. Just use the internet and come as close as possible. Here is a good site.
http://insects.tamu.edu/fieldguide/
Just don't make simple mistakes and do not use the following because they are NOT insects and you would probably be counted against on the following:
spiders, mites, ticks, and milipedes.
Use that website for some ideas and it should give you lots of help! I used a big stirafoam box and pinned needles into the insects and wrote what they were underneath. Good luck. Let us know how you do!