Handle Lock

When I bought my new place, I changed the cylinders in my locks. I have Schlage locks on my door, and I went to Home Depot and bought other Schlage Locks and just changed out the cylinders on my door. I didn't want to change the entire lock because it's an condo complex and the locks have to look uniform and I couldn't find the same locks anywhere, so that's why I just changed the cylinders. I already threw out the old cylinders and just realized a day later that the cylinder is loose. When you put the key in, the cylinder slides in and out by about 1/8". I could swear the old and new cylinders looked identical and were from the same brand. Any idea? Do you think I lost an important piece? I think the old cylinder was 6-pin and the new one is 5-pin, could that be the problem?