Practicing is really the best way to get better. Gauge how much tongue and force with it your boyfriend leaves, then kiss him back accordingly. For example, if he's really active with it, you can let him 'lead' so to say. One person is usually the more passive, while the other takes over.
Your 16 and your overthinking it. Unless you've been lying to him about being with other guys, don't sweat it and just go for it. Go in lightly and avoid using the tongue until you've had a little practice kissing first.
you can always practice on your hand ;) lol jk. is this your first kiss? every body has a fear of kissing badly. all i can really tell you is kinda observe how he's kissing you. make sure you moving your lips in movements with his. don't let him do all the work, no one wants to kiss "fish lips". of course tongue is always fun. but not to much. cause then it just gets nasty lol. just kinda copy his motions a little. you'll get they hang of it real quick :)