As long as the next tests come out the same, you should be fine. Once a tank is stocked, even partially, you should have some Nitrate present. That is the result of the ammonia turning to nitrite, which changes to nitrate. It might read zero for a day or two, but if ammonia is being added (by waste and or deteriorating food), then nitrates have gotta appear.
Make sure you add fish slowly. With past tanks, I usually went one fish, maybe two small, every three to four weeks. If you add too quickly, the ammonia overwhelms the beneficial bacteria and they can't convert it to nitrite quickly enough. You get ammonia readings that way. Those BB numbers will increase as more ammonia is added, they can only do it so fast though. Slow wins the race.