Return the foot if you really don't want it, but I'm thinking your feed dogs might be out of alignment. I had a similar problem last year with my Pfaff and once realigned by the service tech it sews perfectly again.
I've been spoiled by my Pfaff when it comes to the built in walking foot and I think, in ONLY that area, the Pfaff's have a FAR superior walking foot, and in fact, it can be used with MOST of the Pfaff feet...I know, that doesn't help make the Janome one any better.
I really dislike having to remove the regular shank to use the accufeed foot, then remove that to put the other one back on. IMHO, it should have been a snap-on foot like the rest of them! I agree, the Janome accufeed feet are very bulky, but then, the feed dogs are much wider in the Janome, which is a good thing, so guess there is no one machine that is perfect in every way.