Make sure she is very relaxed and very excited. The male penis is built to fit a woman's vagina, it compresses in ways that even the best vibes and dildos don't, but not all women built are the same. She may need a bit of a warm up to help her release oxytocin which helps the muscles of the vagina relax. She can help to bolster her natural release of oxytocin by rubbing your body with the palms of her hands, arms and any part of her body she is comfortable with. Skin to skin contact causes the brain to release all the lovely sex chemicals so get rubbing!

Warming up with gradually larger vibes and dildos will help just as if you are playing anally, so keep working on it...especially just before your special night. Then be sure to go slow and take your cues from her, even the smallest tightest women can surprise you with how much "stretch" the muscles of their vagina's have! Let her relax and allow her body to stretch to accommodate you and it should be fine.

Also remember that you have a long penis, you may not be able to "bottom" out inside her. Again just listen to her and encourage her to talk to you about what feels good and what doesn't. Most girls are a bit reluctant to talk about what feels good to their bodies so get into the habit of asking and really listening.
2 inches is large but not impossible as the vagina has alot more give for girth than length (think birthing babies ) but as long as you go slow and make sure she's both ready and well lubricated...oh speaking of that you might stock up on some nice water or silicone based lube before hand. Lube makes everything better!

Relax and enjoy yourself that's the real advice, if you are gentle and listen you'll not hurt her. Trust yourself you'll do fine, after all, you thought to ask before trying the real deal with her. She's a lucky lady!

Oh absolutely it is normal to have pain when the cervix is bumped. That's why most women agree that length is not the deciding factor in larger penises or dildos, girth is! Some women, like myself, like to feel their cervix touched and/or hit but as far as I can tell most don't. Have you tried to find her "G" spot? Its a spot on the vaginal wall toward her belly button that has a raised "rough" feel to it. If you gently run your finger pad on the upper wall of her vagina toward her cervix you should be able to feel it. When you locate it measure approximately how far it is back and then aim to penetrate only as far as that for a while. As her experience grows you can try going a bit deeper, IF she wants you to.

Misha is absolutely correct about masassaging her pubis as well anything that brings blood to that area will increase the elasticity of her vaginal walls and natural lubrication. I find just a light stroking over the pubic are with finger tips to be an excellent foreplay technique. Just stroke your fingers feather light on the skin just belonw her belly button down over her labia and back up. If she enjoys a light touch she'll love this! If she prefers a firmer touch try doing the same thing with the whole palm and light but firm pressure. Watch how her "lips" swell and begin to "blush" that's a clear indication that blood is pooling in that region.
As you can see the degree of sensitivity to the cervix being touched varies as well as the level of tolerance. Just experiment slowly, don't rush.

Explore her clit gently, if she is ultra sensitive there, play with the hood of her clitoris (the area of skin just above the clit itself) and be sure to use a well lubricated finger or toy. It's the sliding, gliding sensation that is most pleasureable for most women. That's why oral sex is so pleasurable for most women, your tongue is soft and wet! Small circles around the clit might drive her wild as well as gently stroking over it. Get to know her preferences and she'll be more able to relax which will help her when it comes time for the "big event"

Good luck to you both,
~Airen