Note that instructions given are for approx. size S. (My own ones in the photos are even smaller than that… I have tiny hands and arms). If you need a larger size, try going up a needle size - the stitch pattern will allow a variety of gauges, and going up in needle size is probably going to be easier than adding more stitches.
Also note that to really open up the lace pattern, these should be on the snug side.
Some knitters have trouble working out the thumb placement for the 2nd wrister - the first increase round should be as follows:
Work the first 39 sts of round according to chart (last st worked will be the last YO of the last fishtail lace repeat), then mk1, place marker, k1, place marker, mk1, work last 8 sts of chart round. You now have the centre thumb stitch (the one that all subsequent increases are made around) marked, which should help!