The pattern says:
Cast on 45 sts, works 20 rows in g-st.
1st row knit
2nd row purl
3rd and 4th same as 1st and 2nd
5th row inc in 1st st knit to last 2 sts, inc in next st, k1. 47 stitches.
From 1st to 6th sets patt. Keep continuity of patt as set (throughout) inc 1 st at each end of 7th and every foll 8th row to 63 sts .
My interpretation is to knit 20 rows. Then following the pattern I increase 2 stitches on row 25. At this point I have 47 sts. The next rows where I increase 2 stitches each time, are row nos. 33, 41, 49, 57, 65, 73, 81, 89. At row 89 I have 63 stitches.
However, having done this, my sleeve is far too long.
Could someone tell me where I have gone wrong with my interpretation of the pattern?