If your pattern is knit in the round your swatch needs to be knit in the round. If you don't like fussing around with dpns and want a relatively quick swatch that appears to be knitted flat, you can knit your swatch on circular needles. This method is like knitting an i-cord only with a hell of a lot more stitches. When you get to the end of your row you slide your stitches to the other end of the circular knitting and continue knitting with the right side facing you.
Unlike the i-cord, you'll carry yarn across much like a very long float in fair isle color knitting. Don't pull the string too tight or you'll strain your hands with every stitch. Also as you knit, your end stitches will be very distorted so make sure you knit about 10 extra stitches on each end or in this case I did an extra lace repeat on each end.
When your swatch is long enough, tighten the looser end stitches working bottom up with every float then cut the float in the middle so you can lay your swatch flat. I tied the end fringes together to make sure it stayed together. So finally my swatch is done. Here is what it looks like pre-blocking.
Last night, after I washed, blocked and dried it, I measured my gauge in a couple areas to make sure I have an accurate SPI count. I then calculated out the pattern and voila! It's ready to knit. I did my provisional cast on so today I can start fresh with the lace. I'm excited. Happy knitting!