Is there a way to make nostrils straight instead of circular?

Yes there are a number of techniques that can be used to achieve your goals. Specifically, you need a alar-plasty technique that will reduce both the internal nostril circumference and the outer curvature of the nostril simultaneously. This will result in a less circular nostril and a narrowing of the apparent nostril width. My best

Wide circular nostrils can be narrowed and refined either as part of a rhinoplasty procedure, or as a separate procedure. Most of the time with an ethnic rhinoplasty, I am trying to create a more refined tip. Depending on the patient's goals and the physical limitation of the patient's cartilage and skin, once the size of the tip is set, I look at the amount of narrowing of the nostrils required to create a natural balanced nasal tip. 

Yes these changes can be made.  There is no one nose or set of features that typifies a certain ethnicity. There is a great deal of diversity in individual noses. Find a surgeon who demonstrates vast experience in transforming many types of noses.Kenneth Hughes, MDBeverly Hills, CA