WordPress is blowing up my images and breaking the CSS

When I get the image url using the get_the_post_thumbnail_url() function the image is blown up but when I get it from the assets folder in the theme it's working fine.

Blown up image:

Desired image size:

My code:

echo '<div class="col-md-4 mb-3">';
echo '<div class="card blog-post-card">';
echo '<img class="card-img-top" src="'.get_the_post_thumbnail_url(null,'blog-large').'" alt="image">';
echo '<div class="card-body">';
echo '<h5 class="card-title"><a class="theme-link" href="'.get_the_permalink().'">'.get_the_title().'</a></h5>';
echo '<p class="card-text">'.get_the_excerpt().'</p>';
echo '<p class="mb-0"><a class="text-link" href="'.get_the_permalink().'">Read more &rarr;</a></p>';
echo '</div>';
echo '<div class="card-footer">';
echo '<small class="text-muted">'.get_the_date().'</small>';
echo '</div>';
echo '</div>';
echo '</div>';