Good grief. Women are a lot deeper than 3 inches.
How do you think we can get a baby from the stomache area out of our vaginas. Listen, I have two kids, and my husband is about 7.5 inches long...and everything fits well coming and going
Dont worry about this. You should do some research on the female anatomy..it might help.
Or ask your gyn or family doctor, a female confidant, or your mom.
Live life.
Good luck.