Knitting mittens and am a tad confused

I’m making mittens and am now up to the palm shaping of it. I slipped off the extra stitches for the thumb and placed them on a stich holder. Now I’m supposed to continue knitting but I’m a bit confused b/c if I do continue with the same yarn, won’t that make a hole that’s too small for a thumb? I’ve pasted the pattern below and bolded the part that is confusing me. Any help would be GREAT!

Thanks in advance.

GAUGE:

16 sts + 24 rows = 4 inches (10 cm) in St st (k on RS, p on WS) using larger needles.
BE SURE TO CHECK YOUR GAUGE.

STITCH EXPLANATION:

M1 (make 1)

MITTENS
Cuff Using smaller needles and leaving 10 inches tail, cast on 25 (29, 35, 41) sts.
Row 1 (WS) P1, (k1, p1) across.
Row 2 K1, (p1, k1) across.

Rep Rows 1-2 for approximately 2 (2½, 3, 3 ½) inches , ending with RS row. Change to larger needles. Beg with a purl row, work 3 (5, 7, 9) St st rows.

Thumb Gusset: Row 1 (RS) K12 (14, 17, 20); pm; M1, k1, M1; pm; k12 (14, 17, 20).

Row 2 and all WS rows Purl.

Row 3 K to marker, slip marker, M1, k to last st before 2nd marker, M1, slip marker, k to end.

Rep Rows 2-3 until there are 9 (11, 13, 15) sts between markers. P33 (39, 47, 55) sts.

Palm (RS) K12 (14, 17, 20) sts; remove markers, place the 9 (11, 13, 15) sts on stitch holder or strand of yarn; k12 (14, 17, 20) - 24 (28, 34, 40) sts. Cont in St st until piece measures 5 (6, 9, 10) inches from beg. End on a WS row, placing a marker between two center sts.

Top Shaping:
Row 1 (RS) Ssk, k to within 2 sts of marker, k2tog; slip marker; ssk, k to within last 2 sts, k2tog.
Row 2 Purl. Rep these 2 rows 1 (2, 3, 4) times - 16 (16, 18, 20) sts.
Next Row (all sizes) K2tog across. Next Row Purl. Break yarn, leaving a 10 inches tail. Using large-eyed, blunt needle and beg with last st on needle, pull tail through rem sts 2 times, pulling tightly.

Thumb Top With RS facing, return sts from holder to larger needle. Join yarn and k across. Next row P3 (4, 5, 6), p2tog, p4 (5, 6, 7). Work 2 (2, 4, 6) more rows in St st. Last row K2tog around. Cut yarn leaving a tail; thread tail into needle and back through rem 4 (5, 6, 7) sts as for Top, twice.

Finishing: Using tails, seam cuff, palm, and thumb. Darn opening beneath thumb. Darn in ends.

It should be ok. The hole for the thumb will be ‘outside’ the main part that you’re knitting. Basically, up to this point, the thumb part was flat. By knitting across, you’re making it into a circle.