Featured Image Auto Crops

I have the Hatch Theme for my site and suddenly the featured images in my posts auto-crop to 640 x 300 (only a couple posts are unaffected) I have scoured the forums and tried a few different suggestions…

I tried adding a hatch-child folder with php code from the below thread:
http://wordpress.org/support/topic/theme-hatch-change-default-size-of-featured-image-in-a-post
(if someone can explain how this was done that may also be helpful)…

I also manually went into the functions.php file and tried to edit the ratios myself… this appears to bandage the problem…It changes the sizes of the images, but since they all have slightly different sizes so this is not a sustainable solution.

function hatch_image_sizes() {

add_image_size( ‘archive-thumbnail’, 220, 150, true );
add_image_size( ‘single-thumbnail’, 640, 500, true );
add_image_size( ‘category-thumb’, 300, 900 );
}

if this is getting confusing my primary questions are:
1. is there any way to easily fix this auto-cropping? in settings or by customizing my CSS?

2. if I must use the functions.php file….is there a way to make it use percentages, or something that will be more flexible than simply setting the height/width in pixels?

This is an example of the problem: http://stephenbrigidi.com/blog/?p=43

I will happily clarify with any of these questions, and I would be utmost appreciative if someone can help! I have seen people with similar problems but none of the suggestions have worked for me so far.

Thank you!