I have a rather sturdy tubular knit that I want to make a tshirt with.  I have pre washed it.   The only way I can get the tube to lay flat is when it is off grain.   I basted a line of thread up one knit row (it’s not a rib knit).  If I start with that in the middle of the tube, lay out the fabric so it lays flat, over a length of 10 inches the grainline shifts over by 1 1/2 inches.
Can I use the fabric as it came, ie in the tube, or do I need to cut it open along that basted line?