It helps if you use a larger needle or knit looser. Practice it a little - you knit the sts tog but from different sides. The k2tog is with the needle from L to R, k2togtbl is with the needle from R to L.
Do the k2tog in the front first, pulling the loop through loosely (make it long) which will give you room to do the k2tog in the back, before dropping the 2 worked sts off of the L needle.