I think it is okay to politely decline foods you don't care for in most settings. But if expanding th variety of foods you are comfortable eating is something you want for yourself, then you should definitely work on it.
You might seek the assistance of a nutritionist or counselor, or you might be successful tackling it on your own, or with supportive friends or family members. You could have an'adventures in eating' buddy, or you could keep it a private affair. Gradually introduce disliked foods in small quantities as a means of desensitization. Reward yourself for achievements in trying new things.
I personally think the most important thing is to remove any fear, and be willing to try things. It is okay if you don't like it all.