not sure about your comment about the walking foot---you still have to quilt your quilt with fusable batting- it just holds it in place in stead of having to baste- before quilting-
anyway-
what's not straight? the batting or the quilt? lay out your batting- smooth the top over it- press- then flip over- place backing over the batting- smooth- press- be sure to press the edges well- if they are not secure a few pins my be needed- then quilt as desired...once the quilting is done trim the batting/backing- squaring up your quilt for binding.