What point are you at in the sleeve? I'm guessing you are at the sleeve cap, above the point of the underarm . It would make sense to begin working back and forth at that point. On a wearable sweater, you are usually instructed to either bind off a few stitches at the underarm or put them on a stitch holder when you begin the back and forth knitting. I hope that makes sense. You are a brave knitter to tackle something miniature!!!!