I'm 18 yrs old. I had the mirena (levonorgestrel) placed 2 weeks ago. Is there any reason to be scared?

No. Just remember that it only prevents you from becoming pregnant but does not prevent getting any sexually transmitted infections so always use condoms to prevent any of those. Just read the information and the frequently asked questions at the Mirena (levonorgestrel) website fyi. You just need to know how to proceed if having issues with it but otherwise you shouln't be worried about it.