(no subject)

I am so frustrated. Lately, whenever I try to make t-shirts a little smaller so they will fit, (by turning them inside out and sewing up the sides and sleeves) the fabric ends up looking bunched under the armpit when i turn it outside-in again. I never seemed to have this problem before.. I try to make sure that the shirt is smoothed out and pinned and everything before i sew it, but it still happens. What am I doing wrong? Please help!