if you top blocks matched well enough, you top will be square. if it isn't, you can fix it by adding patches to make a pieced border. it'll be fine.
borders do not have to be cut parallel to selvages. some quilters do ... some quilters don't. it'll be fine.
wash it by hand or in your machine's most gentle cycle. drape it over the shower rod to dry. it'll be fine.
when it's almost dry, lay it flat and gently pat and stretch to block it into shape. press until dry. it'll be fine.
do not be afraid. it'll be fine. :wink: