Are you decreasing more rows to accommodate the extra stitches you added in order to get to the correct number of stitches at the end to sew closed? That could cause a more pointed look. I find that many mitten patterns are what I call "nose-pickers." In those cases, I will allow a bit more length after the thumb, and sacrifice some of the decrease rows so that the top of the mitten is more rounded. For example, if the pattern says to decrease until there are 4 stitches on needle, I will sew it shut when I have 8. The end is not pointy. Experiment. You will find a happy compromise.