Temps and humidity are fine.
Is your soil draining well? Does your container have adequate drainage holes? Sometimes, the TOP of the soil looks dry, so it might prompt you to water more....but a few inches down, it could be muck.
EDIT: For what it's worth...I always start my plants in party cups filled to about halfway with soil. I moisten the soil to the "perfect" moisture level and then I weigh the container. When the container starts to get light, I know I need to add water....And I only add as much water as needed in order to bring the container back up to that "perfect" weight. So, no matter how dry it might look on the top, if the weight still indicates enough moisture in the soil, then I just leave it alone.
Your container is larger and you have a lot more soil than I would use for a plant that size.