Getting into a lab as a undergrad varies in difficulty. At some smaller colleges there are lots of research opportunities for undergrads. But at others, it is heavily grad focused, so not many undergrads can get into a lab. Also the productivity of the PI, grant funding, geography, and other factors come into play.
But having prior research experience will definitely help. The biggest factor that can help is networking (SfN). Having an introduction from someone in your network can make a big impression.