Hello, and welcome to KnittingHelp.
Although the pattern suggests knitting on circular needles, I don't think you're ment to knit in the round. Instead you're suppost to knit flat (by turning your work at the end of each row). If the pattern refers to 'Rows' instead of 'Rounds' and/or RS or WS it's ment to be knitted flat. Clrcular needles are often recommended for large items, like afgans, as they are big enough to hold the stiches and keep the weight central or balanced.
Sorry to be the bearer of bad news, but it looks like you'll have to undo your work and start again.