Why did the quality assurance test of the culture media fail?

Hello. I work in a microbiology lab and we've been trying to test the quality of new batches of Bacillus cereus agar and Nutrient agar. We used the quantitative method (ecometric method) in which we brought an inoculum (from a 4-hour pre-incubated culture of Bacillus cereus in BHI broth) to extinction by streaking on divided plates (A1-B1-C1-D1-B1-C2...etc) without recharging the loop. We just observed the results after 18 hours and strangely the colonies are very spread and the growth only gets more intense towards the center of the plates (A5-B5-C5-D5), What have we done wrong and how can we avoid this in the future? How can we get clear and identifiable results?