In the end I cut down the velveteen to the length of the voile and sewed them together - without pinning. Next time I will most definitely pin - because, blow me, by the time I had sewn both side seams (using a walking foot) - the velveteen was nearly an inch longer than the voile - AGAIN! Another trim with the rotary cutter was needed.
Fortunately I had the perfect colour thread in my box that matched the voile exactly for the hand sewing part at the end.
The size is fine - perfect if you wanted to wear it unwrapped (though in which case I think I should maybe have added the moebius twist) and a short neck warmer when twisted into two loops. The neck warmer is what I need. I sit by a radiator at work - but I also sit by a window, and so far the window is winning.