You're going to have a jog when switching from a purl round to a knit round. What I do when going from knit to purl is slip the first st of the round, purl around and do the slip st at the end of the round. Then slip the next stitch and knit around, knitting the slip st at the end. Slip the next one, purl and purl the slip st at the end. This can move your beg of round over a little, but once you start working in stockinette st, you can go back to the original beginning.