I'm in the straight section of the clapotis and misread row 8 of the instructions for 2 repeats where you are supposed to drop the stitch , "pick up the top bar to form a new stitch, knit this and the next through the back loop". What I did was knit BOTH of them TOG through the back loop! When I realized I was missing a stitch on the next row, I just added a stitch. At the time, I didn't think it would matter because it wasn't next to a stitch marker (so shouldn't be one that would be dropped later). Now, I'm not so sure, because now I have to start adding stitch markers at the other end again! Am I going to be in for a big surprise later when I drop stitches, or it going to be okay??

As long as you added it above where you knit them together you should be okay. You could have skipped the p2tog at the end of the following row too.

Darn - nope, I only added it when I realized the mistake, so I added it on that row. I guess that means I'm going to need to rip out QUITE a few rows, huh?

Yeah, in order not to mess up the other sts, it should have been added at the same spot. If you're going to go back, then you can do it without knitting them together.