Expanding knitted afghan pattern

:?? I am trying to expand a pattern to create a 36" (+/-) baby afghan. I have a pattern for a Double Parallelogram which creates a 12" block. I did multiples of the original cast on of 54 sts by 3 for 162, plus I wanted to have a garter stitch border on each side so I added 10 additional stitches for a total to cast on of 172. After knitting 8 rows for the bottom edge, I worked the pattern row and came up 3 or 5 stitches short (I discovered this last night and was very frustrated.).
Yes, this sounds like a case ‘are you sure you counted correctly’. However, I also tried expanding another pattern 3-times and had the same problem with it.
I hope someone will take the time to help me with this. I love to knit, am to poor to buy new patterns and figure I should be able to create an lovely baby afghan by expanding some patterns I already have. Any help will be appreciated. Thank you. Skc

Does the Double Parallelogram pattern have a line that says stitch pattern=
X + y stitches? Patterns often will not just be doubled or tripled. A pattern may have a stitch pattern of, say, 5 + 2, which means you’d need to cast on a multiple of 5 plus 2, so, 7, 12, 17, 22, etc.

how do you do the Double Parallelogram stitch I saw a sample on the knittingdaily.com and I really like it.

I went through the same thing on a knitted afghan pattern that I wanted to widen. I ended up ripping out 3 times before figuring out the pattern stitches as opposed to the edging. You may need to look at the original pattern and see if some of those stitches you multiplied are only for the edges.