Yes, that's how I read the instructions your pattern gave--you do the decrease over 3 stitches. So you would continue doing what the woman does on You Tube with one more stitch. That will give you one more loop on your hook to pull through at the end of the decrease. You will have 4 loops on your hook, while she only has 3. At that point you have gone from 3 stitches down to 1. My afghan pattern does a 3 stitch decrease exactly like this. It just depends on how many stitches need to be decreased.
And it does appear that you do this decrease twice, side by side. You are doing a ripple--notice that you also do 3 dc in 2 chains, so you should end up with the same number of stitches at the end of the row. You are increasing at the top of your ripple--2 stitches become 6--and decreasing at the bottom--6 stitches become 2. You continue to do this across the row.
After you finish this first row, it will become much easier to see. The foundation row is always the hardest!
Keep us posted!