So i've been trying out the cornelli lace technique using royal icing. On the advice received here on CC i'm using icing of a thin consistency, with tip No 2, but my piping seems to spread slightly and doesn't hold a firm shape. Can anyone suggest what i'm doing wrong? Is my icing too thin?

Yes your icing sounds too thin. Should not be spreading on you. Or you could change to a 'one' tube. But if you do you would want to seive your icng so no lumps clog it up and break your heart. Or you could just thicken what you do have.