You mentioned rushing the drying step warped your journal, so what part did you speed up? I've found that even a little hurry can mess up the paper. How are you slowing down now?
Read somewhere that the paper type matters a lot for warping. Thicker mixed media sheets tend to buckle less if you let them air dry flat first, lol. Been trying that method with a cold press pad underneath. Might be worth checking if your journal paper is similar?