I wouldnt worry about it. Its not usual but its whats happening. Just wait it out, when you can cycle out 2ppm to zero ammonia and nitrite in 24 hours you are cycled enough to moderately stock fish.
2ppm is more ammonia than a tank full of fish will produce. Possibly the gravel you used hasnt seeded enough microbes to cycle out all that ammonia, but has enough to cycle out the nitrite.
Skip a day ammonia dosing. See if the ammonia goes down if you arent adding any new.