Most Helpful Guy
I was anxious at first myself, but after my first kiss it passed. Also, speaking as someone who has had social anxiety it sounds like you have a really bad case and should consider both therapy and medication.
Most Helpful Girl
The best advice I can give to you is to just relax and enjoy the intricately blissful sensations of kissing. Lets break it down logically: Kissing is not the end of the world. The Earth will still keep turning :P The kiss won't magically reverse or negatively change the relationship. So don't put this crazy pressure on yourself. Be gentle, patient, and gracious with yourself. Don't expect yourself to be a master as a beginner who's still learning. The more you adopt this connection the more those anxious nerves will transform into eager excitement. :)
Confidence is a superpower. It makes us feel like we can achieve the impossible like moving mountains. If you want to gain a certain type of experience or know of a certain result, then you absolutely have got to be confident, self-loving, self-appreciating, and let your passions overwhelm your fears. Trust me, I will not steer you wrong ;)
So next time, instead of being so anxious and letting nervous thoughts bounce around in your mind, focus on enjoying the unique shape of his lips, let your hands innocently roam and admire his physique, gently exploring his chest or the unique curve of his jawline. Graze your fingers on the back of his scalp just above his hairline like wind tracing through a field of tall grass. Really lose yourself in the moment. Submerge yourself into the chemistry you two have and emphasize on elevating the sensations rather than being paralyzed and too afraid to explore the potential. Good luck!