The opening to your cervix is not even CLOSE to big enough to accomodate a tampon (so, you've heard some very incorrect info). Put your fingers in there and feel the front of your cervix, if you never have: that little dimple is the opening. It's TINY. All you need to do right now is reach in and feel for the tampon. Your vaginal canal is no more than about six inches deep, so if it's there, you'll feel it.
FYI: you should NOT use tampons when you are not menstruating and you should NOT use tampons when you're having intercourse. Both put you at a sizeable risk of TSS, and the latter ups your STI risks as well as puts you at risk of some bruising, abrasions and serious discomfort.
If you want to have protection from an oncoming period, you should use a pad until you are actually menstruating.
Lastly, drinking to the point that you can't remember things clearly means drinking too much -- it's an especially bad combination with sex, as people under the influence of booze tend to have some serious lapses in judegment.
Editor and Founder, Scarleteen
My epitaph should read: "She worked herself into this ground."
-- Kay Bailey Hutchinson