well since you already have the cycle started, why would you want to start over?About the same thing happened to me, i bought about 20 fish to cycle my tank, but my Ammonia just wouldn't go down, when i had lost all but about 2 zebra danios, my tank finally cycled.
You could go get a raw shrimp from the grocery store and throw that in to finish the cycle, in the meantime, get a test kit and test for Ammonia, Nitrite, Nitrate. I would say since you've already got it started, you may be close to the end of your cycle,Im sure you've already got some good bacteria growing in there, and i don't see any reason to get rid of that. i wouldn't start over, go ahead and finish the job, if you start over its just going to take twice as long. You've probably got the ammonia and maybe some nitrite in your water and that's whats needed to cycle.