I have made two sweaters that require you to put stitches on aside for the sleeves and continue with the body. When I go back to finish the sleeves by then knitting the stitches I have set aside on a loop of yarn, I get a hole under the armpit. Am I not knitting the first round tightly or what? I am about to that stage again on a shrug and would like to prevent it happening again. Thanks for your help!