Hallow Dear,
Since she is virgin, what you felt inside the opening of her vagina is
hymen.
Hymen is a naturally existing fibromuscular septum situated just inside the opening of vagina. This septum gets torn most of the times during first intercourse, though other activities like riding on two wheelers, athletics, heavy exercises, sitting astride, horse riding, tree climbing, etc. also may be responsible for the rupture of the hymen.
If her hymen is still unruptured, you will have to rupture it during first intercourse by your penis. You may try increasing the opening of the hymen by your finger(s) before inserting penis. It will cause some bleeding, it is normal and nothing to worry about. In some girls, the hymen is very tough to be pierced by penis and requires surgical incision. If that is her case, you may report to the Gynaecologist to help you out in this matter.
Please do not get disgusted. This is not
vaginismus. In vaginismus, there is a lot of apprehension and pain, which she is not having.
I would definitely like to help you out. If still there is any more difficulty, you may ask me Direct question.
Dr. Nishikant Shrotri