In growing lilies in pots there are a few things to consider:
1)You don't want a mix too heavy in peat moss. Those mixes tend to stay wet too long and the bulbs don't do well.
2)No matter what mix, you don't want to over water.
3) You want to use a larger pot so the bulb can be planted at the proper depth and so the pot won't tip over when they get as tall as they do.
4)Planting shallow growing annuals, as a "ground cover" can help shade lily roots in the pot.