Portfolio item page column size problem

I am creating a post from portfolio section. Uploaded images, set one of them as featured image, set the format as gallery. Everything works and positioned. I understand the portfolio post page is naturally divided as two column. But right now the slider side of the column take about 2/3 in the post, the other side of the column is about 1/3.

I am trying to fix it as the two column as 1/2 1/2 or the slider side even smaller, like 1/3 instead of 2/3. I have been looking here for long time really didn’t find an answer. Should I change something from single-portfolio.php?????

Please help. Thanks.