Does a penis not being sercomsized look smaller then what it really is?

Yes and no. If the tip of the foreskin is tight, the penis may not extend completely and look shorter than if it were circumcised. However if the opening is normal, there would be no difference.
Penis size. Obesity can cause this but the foreskin has nothing to do with size. The foreskin extends and unflolds when the penis is erect allowing the glans to protrude without recruiting the scrotum onto the shaft as happens with circumsized men. This could make it look longer.