Fixing the movement by allowing the player to keep the R/L button pressed was the second thing I fixed after the jam: https://github.com/renato-grottesi/arduboy/commit/1d7ecf7cc63a259983ecdd374d531c51e0453ed3
I'm thinking of perhaps increase the speed to 2 pixels/s when the button has been kept hold more than 2 seconds and to 4 pixels/s after 5 seconds to make it less painful. And I'll implement another suggestion about double clicking R/L to move to the next free spot to build.
Thanks a lot for playing and for the feedback! :-)