The pedal coming off on a new bike is a clear assembly defect. It is a mistake with ANY product to try to "fix" it when still in warranty, as it muddies the water regarding what happened first. If the retailer is at all reluctant it gives them an excuse to not warranty the item. Normally such and occurence would call for the seller to at minimum replace the pedal, and the entire crankarm if necessary. You can try the suggestions above but you may want to go to the retailer first to see if they will agree to correct the problem.