No worries! The game automatically gives you a random name in the Leaderboards section. If you already have friends in your Friends List, their names will be automatically updated too. With this name, you can easily find yourself in all Leaderboards types! Just tap on the "Find Me" icon and your name will be centered among all the Leaderboards' entries!
Remember: When you log into any social network, the Profile name will be changed to your name from that social network.