My husband has a penis size 3" he feels so embarrassed. What could b the possible treatment except surgery??

Need to work. Around these issues with reassurance. There really aren't any effective nonsurgical techniques. If your husband has extra body fat, including fat around the pubic area, losing weight may "expose" more of his penis. Even the surgical techniques are not particularly effective.
Exercise. It may be familial. Exercise the penis regularly....that may have to help him on that.