I’m not exactly sure what you mean when you said,
"but need to know if I have completed 6 purled rows which side of my needle should my completed work be on…"
You may be talking about the back of a knitted and purled piece (stockinette–knit a row purl a row, repeat), or maybe you purled 6 rows. If you purl every row you will get garter stitch just like you would if you knitted every row. Most people prefer to accomplish this stitch by knitting every row, because they prefer to knit over purling. But if you like to purl you can do it that way.
I’m thinking about as you begin your self designed scarf (I love it, go for it) and you are trying to decide which side is the “right side” you might take a good look at the effect you get right at the beginning of your piece. If you do garter (knit or purl every row) it looks a little different right at the beginning on the two sides, after that it looks the same on both sides. See which side you like the looks of the best and decide that that is the right side. There are also slight differences in the way most cast ons look on one side or the other. Pick the side that you like best for that as well. If you’re doing garter, the little difference that you get on each side because it is the first row will probably be a more noticable thing than the side of the cast on. But it’s your scarf and you can pick the side you like best to be the “right side”. With a scarf both sides will show, but if you do anything that looks decidedly different you will want the side you like best of that to be the “right side”.
If you’ve been doing garter and want to switch to stockinette do a purl row so that the purl bumps end up on the side you have designated as the “back”, and the flat vees of the knit stitches end up on the front. Unless you want it the other way. LOL Reverse stockinette (the back, or purl side of the stockinette) can be chosen as the focal point of a piece as well as the “normal” side. This is all part of the fun of designing. Have fun.