cast on question newbie

[newknitter80]

My yarn has ended half way through my scarf. If I cast on my right needle it will create a new stitch and I will have 13 stitches as opposte to 12 I've had. How do I keep twelve stitches in my pattern and add my new yarn? I hope this makes sense...I'm still new to knitting this is my first project.

Thanks

[Nanaof6]

Knit Picks shows the Russian Join,

http://community.knitpicks.com/notes...-_Russian_Join

Since I have found this I always use it. It's so easy and no lumps or bumps.