Help needed please!

I’m knitting a baby cardigan with some lace at the bottom. I have cast on 141 stitches, and then I have to knit 1 then repeat the following pattern until the end

Yfwd, s1, k3tog, psso, yfwd, k1

And then I should end up with 113 stitches, but when I did it I only ended up with about 80.

I assume I bring the yarn forward, slip a stitch over, move the yard back to behind the right needle, knit 3 stitches together, passed the slip stitch over, bring the yarn forward and knit another stitch…

Am I doing this right? If so, why would I end up with so few stitches???

Welcome to KnittingHelp!
British patterns give exact directions for a yarn over: yfwd, yarn round needle, yarn over needle where American patterns use the single yarn over to cover everything. In the case of this pattern, the yfwd is a yarn over.
For this pattern, bring the yarn forward, slip one, move the yarn to the back [I]over[/I] the right needle to k3tog, pass slip stitch over, yarn to the front and [I]over[/I] the right needle to k1.

You’ll increase 2sts every repeat and decrease 3sts so that’ll give you a total decrease of 28sts (141–>113)

It worked!! Thank you!!