Confusion w/ pattern

[tdussell]

I am a new knitter and am TRYING to make a baby blanket on circular needles. I have a question in regards the pattern I am using.
My pattern indicates that:
Row 13 - K3P3K3 P9 then *K9 P9* until the last 18 stitches, place maker then K9, K3P3K3
Row 14 P3K3P3 K9 then *P9 K9* until the last 18 stitches, place maker then P9, P3K3P3
Okay so now I have 2 stitch markers on either ends of my blanket indicating where the last 18 stiches are.
Now the pattern says
Row 15 - Repeat Row 13
Row 16 - Repeat Row 14
Am I placing new stitch markers or just slip the existing markers?
The next two rows are the same as Row 13 & 14 but says slip marker (instead of placing marker)
Am I getting myself too worked up about the stitch markers and basically all I need to do is place/slip them as they are so that they indicate where my pattern does a change (ie P3K3P3 pr K3P3K3)

Please help me get piece of mind before I lose it!