Hi, and thanks for your medical question on eHealth forum!
It could just be that you were not sexually very stimulated. It cana lso be due to muscle or nerve injury or due to infection. You can try pelvic floor exercises to tighten the vagina. Your gynecologist can suggest some. One such exercise is to hold breath and pull in your pelvic floor muscles as in holding on to urine.
In some cases the vagina is tightened surgically. Do consult your gynecologist regarding this. Hope this helps. Take care!