As Sue says, if this is your cast-on, just keep going or use another cast-on that doesn't allow so much yarn to pull between the stitches at first. (You might also try making sure that you're working with the yarn and stitches right at the end of the needles, right before where the tip starts.) The process of making the stitches will pull the extra yarn between the stitches at first, but the process of putting the needle between the yarn and the holding needle will pull it back out -- you'll also find that around row two and three, the extra yarn starts pulling back into the stitches.
OTN: Eyelet Chemise in Handmaiden Sea Silk (colorway: Midnight). Still. And a purple Donegal Tweed set of fingerless mitts, to try out my new Hiya Hiya interchangeable needles.
Latest FO: A shrug for an Anthropologie swap in beautiful Casbah sock yarn, in Cedar, a dark green semi-solid, my own pattern. Also a quick Noro Silk Garden neckwarmer for my friend Aideen, in a vine lace pattern.
My knitting blog, Another Long Yarn