I need help with the sleeves for my first sweater

I would say that I am an intermediate knitter. However I’ve never done a sweater and I’m not good at adjusting the pattern, correctly. My main problem is I don’t think I have enough yarn to do 2 full length sleeves. So I wanted to make them a three quarter sleeve. Can ANYONE help? Here are the directions for the size sweater I am working on:
Cast on 45 sts.

Rows 1-6: Knit.
Row 7: (WS) *K11, m1, rep from * 2 times, 32nd K12-48sts.
Row 8: Purl.

Continue in stockienette st, inc 1 st each end of needle on 5th and every following 4throw to 66 sts.

Continue in stockienette st, inc 1 st each end of needle every following 6th row to 86 sts.

Cont even until work from beg measures 17.5 in, ending with a WS row.

Shape Raglan

Bind off 7 sts beg next 2 rows- 72 sts.

Work 2 rows even.

Next row: (RS) K1, SL1, K1, psso, knit to last 3 sts, K2tog, K1.
Work 3 rows even.

Rep last 4 rows 0 times more, 70 sts

Next row: (RS) K1, SL1, K1, psso, knit to last 3 sts, K2tog, K1.
Next row: Purl.

Rep last 2 rows 27 times more- 14 sts.

Next row: (RS) K1, SL1, K1, psso, knit to last 3 sts, K2tog, K1.
Next row: P1, P2tog, purl to last 3 sts, P2togtbl, P1.

Rep last 2 rows 0 times more- 10 sts.

Leave rem 10 sts on a st holder.

Shortening sleeves can be a little tricky. Changing them is easier if it’s worked from the top down.

Since your pattern works from wrist to shoulder, I would skip the first few rows (I counted 45 rows) and start where it says 66 stitches. Cast on 66 instead of 45. Work the first 6 rows in garter stitch and then follow the instructions…

Continue in stockienette st, inc 1 st each end of needle every following 6th row to 86 sts.

Cont even until work from beg measures (change measurement to the desired length from the bottom of the arm opening) ending with a WS row. Then proceed to the raglan shaping.

This may end up with shorter sleeves depending on the row gauge. 45 rows is a lot to skip. For example: If your gauge is 5 rows/inch then you’ll be shortening the sleeves by 9 inches ending up with a sleeve that is roughly elbow length.