No, you did nothing wrong. It's just not really a plant that is meant to be a house plant. They sell them to be the same as a bouquet of cut flowers - to last a short time and then be thrown away. At least as a plant it lasted longer than it would have if it was cut and in a vase.
It's a waste of a plant, and if you had a garden outside where you could have planted it as soon as you brought it home, it may have grown for another month or two. But it would never have made a good plant for you to keep long-term. It needs to be outside in the full sun in a garden where it can make a huge root system.
