It should look normal again. Once you remove the width it will return to the size you had set in the options, which was 150px x 150px in your case. The quality of the image won’t be affected, it will show up exactly how you upload it, and at the size you specify in the options.
The “featured img” width made the image look stretched since it was showing the 150px version of the image (thats what you had it set to).
