Tips For an 18 year old guy with premature Ejaculation?

I imagined my first time to be a wonderful experience but it ended up being a disater. I'm 18, good looking and outgoing. I have been seeing a girl i really like for about two months, i've known her for years but only recently had the confidence to ask her out. A few days ago she told me she had a free house and asked me if i wanted to stay the night. Naturally i jumped at the chance and went round straight away. When i got there we chilled out for a couple of hours, watched a movie and then decided to go for it. I told her i wasn't experienced but i still had visions of lasting atleast 5 minutes! We teased eachother for about 20 minutes, kissing and cuddling etc and everything was going perfectly. I then started to take my boxers off and to my horror, i realsied that i had already ejaculated. I was deavastated, particularly as my girlfriend looked so gorgeous in front of me. I tried in vain to get it back up but i just couldn't do it, in the end she just said that it was Ok and she didn't mind. She was really nice about it, but i was absolutely guttered and went into a state of depression, alls i could say to her was how sorry i was. What can i do? She says she wants to try again and i really want to, but i'm terrified that this will happen again. I'm still a virgin, i've watched porn on many occasions and masturbate almost daily. I really want to make it up to her but i'm worried that this will happen again. Can someone please help me..