Be calm, think rationally.
If it goes well, great! You may have met a new friend or boyfriend or friend with benefits or activity partner or whatever you two decide.
If it goes absolutely horribly, so what? You're not obligated to see or talk to the guy again. No one else in your life is going to know any of the details about a lame date unless you tell them, so there can't be any judging or whatever. You won't have lost anything because you didn't have a connection with the guy or a relationship or anything. You'll be right back where you were, as whole as you've always been, nothing more nothing less - so who cares?
Even if it goes terribly, you'll have at least made an effort and tried! You'll have met someone new, gone on a Valentine's date, ruled someone out that you don't want to be with, learned to calm your anxiety about these things and get outside your comfort zone a little bit... so many positives to having gone through the process even if the end result isn't ideal.
But instead of worrying about what could go wrong, maybe you should try focusing on what could go right? I mean, what if the guy is totally awesome and you click with him and enjoy each other's company, share some great conversation, smiles & laughs all evening? Think happy thoughts and happy things may happen... focus on the negative and you'll manifest that reality because you'll make yourself so nervous and anxious and worried and so forth - so don't do that!
Try going for a run/doing some exercise to lift your mood a little, take a hot bath, enjoy some peaceful music, spend 20 minutes on peaceful meditation, spend a few minutes doing some "power poses," to boost your confidence by literally altering your hormone levels in the process... and then go out with the intent to enjoy yourself even IF he turns out to be someone you're not interested in seeing again. Then you'll end the night with a smile having accomplished a whole lot of good things even if a second date or boyfriend isn't the end result.
Relax, enjoy.
You are right. I admit this soothed my anxiety a bit. Because we were both exhausted of our day we decided to move the date to sunday. So now I have two days to warm up to the idea which makes me feel a bit more comfortable.