It seems that a lot of us get crabby to varying degrees while on the cleanse. I can't help but think it's the result of "stuff" getting worked out of our system physically and emotionally. You may be releasing old stress or issues or toxins, and that's a good thing! Just count to 10 and don't release them all over your family! ;)
Someone on this forum has oft advised not to end a fast on a "low". I think that's great advice, and pass it on to you.
Take it day by day, stop when you feel it's right for you - that you're moving TOWARD something (better health) instead of AWAY from something (the crabbiness).