Help! Tempering Chocolate.

I’ve decided to try and make Easter Eggs this year and I’m trying to temper chocolate for the first time. I’m using Callebaut milk chocolate and the seeding method. I’ve been using a metal bowl and heating the melted callets to 45 degrees, removing from the heat and adding 30% of the total weight in chopped callets, mixing constantly until the temperature reaches 27 degrees (approximately 15 minutes) and then reheating to 29 degrees. The room I’ve been working in whilst cooling is 21 degrees. I’ve had 5 attempts so far and none of them have been in temper! Any help would be much appreciated.