You are using get_field and you should be using get_sub_field
<?php if ( get_sub_field('prod_gallery_wide_image') ): ?>
<div class="gallery-grid-item-width2">
<img src="<?php the_sub_field('prod_gallery_item');?>" />
</div>
<?php else: ?>
<div class="gallery-grid-item">
<img src="<?php the_sub_field('prod_gallery_item');?>" />
</div>
<?php endif; ?>