OK GUYS WHY! 
i had my first ld just last night
ok here how it began
it was 2:50 am (i checked before i sleep) and i was using the computer, suddenly i fell asleep ( dont know how cuz it just went blank) and i was in a SP but!!! here is the best part i just got in a dream in like 10 sec it WAS FAST! and of course i was lucid fast
it began in my room then i thought of a japanese sexy lady 
( im a pervert 
) and boom she was there in my room and then i thought her to be naked but WTF she just keep on flashing with different clothes on!!! then i teleported at my school then i saw another jap girl crying with a boy shot and bleeding in her hand but of course i was lucid so i just rushed to her and kissed her 
then i woke up AND IT WAS JUST F****** 30 secs!
i do some RC when i woke up and the time was 2:51 its FAST WHYYYYYYY
Maybe you just got too excited. People tend to get excited when experiencing lucid dreams and wake up. Kissing a girl, like you did may have caused your excitement too. Don’t worry though, keep your emotions calm during the next LD’s and they should be stable & long. First dreams often tend to be short. Mine’s didn’t last even for a minute . To stabilise a dream you may also use techniques like rubbing hands or spinning around. Also make sure you don’t get woken up by noise, as the place where you suddenly fell asleep might have been noisy.
Yes, the key is in keeping your emotions in order. I know how exciting first moments can be but that’s the mistake and how you instantly thought about japanese sexy lady, and I believe there were some other thoughts and things you wanted to do…
BUT when realizing that you are in a dream try to stop. Try to see where are you and what you are doing, because by doing that you will stabilize your dream and your emotions… Then you can start with something smaller… When you have you confidence that you can do more demanding things!