Ooops, sounds like you didn't blend/grind the batter enough. When the urad dal is almost the consistency of whipped cream, you have reached the right consistency. Be sure to use a powerful (750+ watt or more) grinder or blender or a table-top wet grinder for the best results. Also, please be sure to soak the urad dal for at least 4 to 5 hours or even overnight. If the dal aren't well soaked, they will not grind to a soft, fluffy batter. Ensure that you use fresh urad dal in its shelf period. Aged or old urad lentils will take a lot of time to grind or blend and can also make the vada dense or hard.