No guts, no glory! But then again, no second, third, fourth trip to the lumberyard......
Find something cheap to practice on. I like to use the 4-7 inch wide x 96 inch long offcuts left from a sheet of MDF. They machine great, are cheap, and can give you a good idea of what your profile is set to. I'm always impressed how just a slight change in bit height can give a whole different look.
Poplar is another good wood to practice on. It's a relatively cheap wood in my area, and it's easier on the cutters than MDF.
Save your scraps, they're always good for setup or practice!