Since you mention it's a blanket, I think you want to knit something flat and only need the circ to hold the large number of sts. You don't want to knit in a circle (a tube like a sleeve or the top of a sock).
It sounds like you kept going in the same direction after you finished your first row, instead of stopping and turning (switching which needle point was in each hand). You don't have to start over from scratch, but you will need to go back to the end of your first row, to 'unjoin' your knitting.
Since you're a 'newbie', the best way at this point is to just undo each stitch, one at a time. Pick your knitting up like you would to keep knitting, with the yarn hanging behind the work by your right hand. Now swap what you're holding in each hand so that you turn your work and the yarn is now on your left and at the front. If you pull the yarn, you'll see the last stitch you made tighten around the left needle. Place your right needle tip into the st below the one on the needle, and slide the stitch off of the left needle. Pull the yarn and you will lose that stitch, but the right needle has the one below so all is well. The yarn is still falling from the left needle, from the st closest to the needle tip. Keep undoing sts until your knitting isn't joined anymore.
Now treat the needle points like they were individual needles that just happen to be joined by a cable. Switch which 'needle' is in each hand every time you finish a row. You'll know it's good because the yarn will be hanging off your left needle, from the last stitch of the previous row and you'll be using it to knit the first stitch of the new row.