Make sure to chill the crème brûlée for long enough. They need to chill for at least 2 hours for the right texture.
If you don't want to buy superfine sugar, regular granulated sugar will work as well. It will just take longer to caramelize.
In a pinch, you can also caramelize the sugar under a broiler in the oven. Place the oven rack as close to the top of your oven as possible and broil for 5-10 minutes, occasionally rotating the pan, until the sugar is evenly melted and browned.