I am seventeen and still have my foreskin. Can it stop the growth of the organ?

No. Make sure you can retract your foreskin all the way back to the crown of your penis. At your age it is critical to clean the head of your penis daily.
No. The penis, under homonal stimulation will continue to grow. The foreskin is very elastic & will accommodate penile growth. The foreskin could be come tight with erections & cause some discomfort & may not be easily retractable or retractable at all. Should you have a prblem with the foreskin, see your pcp or see a urologist and discuss this. The foreskin is normal, but you may need some help.