Want some medical advice? You two do not sound ready as you do not even know how to use lubrication.
i think you need to take things slow. you need to make your girlfriend really relaxed and comfortable so things down there relax and so that she has more moisture down there so you will fit in easier. try fingering her and kissing alot. that always makes the juices start flowing more. you can also try oral sex to moisen things up.
and if you are using condoms, and you should be to protect against pregnancy and STIs, it can always use some sort of lubrication. try kj jelly or ansel personal lubricant.
hope that helps and next time is better for you both. :)