4inches is an absolutely perfect size, anything below 3 inches is defined as small as per the journal of sexual medicine. So please don't worry. However the only way to increase the size of the penis is the penis traction method. That's the only scientific way proven thus far for enlargement of penis size upto an inch in length and girth.
Next Steps
Please consult a competent certified sexologist for advice and guidance
Health Tips
Do not fall for false claims of penile size increment which aren't scientifically proven.