Crochet dilemma

I like to think of myself as a fairly experienced crocheter, but almost all my experience is in thread doilies, worked in the round with small steel hooks. This has given me a rather cavalier attitude to gauge, because really, who cares exactly how big a doily is, as long as it's pretty? For various reasons, however, I want to make an afghan -- something fairly straightforward and with no sewing up, preferably. Last night I thought I had it all lined up, and I embarked on a simple ripple pattern. ( Of course, it turned out not to be quite that simple. )