If you tend to be a loose knitter, then you might want to try going down a needle size to see if you can get gauge with the lace pattern as listed in the pattern. If you tend to knit tightly, then try going up a needle size.

If this doesn't seem to work, then it might have something to do with the way you tension your yarn. I tend to wrap the yarn once around my little finger then up over my pointer finger and to the needle. There are so many ways to hold your yarn, and there isn't a right or wrong way to do it -- just the way that's easiest for you.

Cast on for the first sleeve, work across in the lace pattern #3 (row 1), then cast on at the other end and purl across (row 2). On the next row (3), you just work across the whole row in lace pattern #3 row 3 and continue with the pattern as you go. Yes, there is a one-row difference, but it's not going to show, as the first row gets sewn into the seam.

The "back of hand" stitches are those which will be worn across the back of the hand when the mitts are finished; in other words, the lace half of the knitting.

I would still block your garment even in acrylic yarn. Some acrylics take better to blocking than others, but I'd say there's always a better result after blocking.