Tom what some pros do when fillet brazing is to make a 2nd pass while the joint is still hot from applying the brass on the 1st pass to even it out and perfect the shape of the filler. It makes sense to practice on the same joint again adding brass or just playing with the fillet and getting a better feel for shaping it by keeping it in the puddy stage. You are going to throw it away later so whatever you do to it won't matter. The purpose of practice is to get a feel for handling the torch. It takes a long enough time to set up a practice joint so get as much use out of one as possible.
I recommend buying some .035" wall tubing for some practice before you get to your real frame. That is going to be thinner than your junk frame tubing. You will want to get a feel for brazing thinner tubing so you don't mess up when you jump up to making a frame.