Formatting cover photo size

Since updating to the latest version of word press, I am unable to format my cover photos correctly. No matter what I change the dimensions to they stay wide and distorted I used to be able to change the dimensions but it doesn’t seem to work any more.

This is the html I have for this page http://yorkshiretots.com/walking-with-tots/

[blog category=”17, 18, 32″ images=”true” image_width=”300″ image_height=”300″ post_content=”excerpt” excerpt_length=”50″ show_date=”true” author_link=”true” author_avatar=”false” comments_link=”false” show_category_list=”false” show_tag_list=”false” posts_per_page=”7″ paging=”true” read_more=”Read more….”]

As you can see, the photos are not 300 by 300. I’ve tried disabling the plugins but it didn’t help. If anyone has any ideas for me I would be grateful.