Let your directional pad/stick drop to neutral after cancelling the 2NDC.
You're getting the nomad dash because you are cancelling the 2NDC by pressing Back + Block. The game is interpreting the back input as a buffer for Nomad Dash when you press Forward + 4 since the input for Nomad dash is Back, Forward + 4.
You could also try cancelling the back, forward motion by pressing an alternate direction prior to pressing Forward + 4 (ie: 2NDC/down/forward +4).
