Well, thanks for the good wishes!. Now it is done
Things were completely different than I had planned. Here in Germany (or at least in Bavaria) they celebrate weddings different than in Spain. The wedding ceremony itself was at 12. Then, on the hotel, where all the celebration was done, first we had some drinks and snacks at about 13. Then at 15 some cakes and coffee. And then the dinner was at 19. So, at about 17:30 I got to the piano, thinking just on testing the waters... But people were around that area, talking and enjoying some rest, so I continued playing for about an hour and a half. I was completely calm and very happy due to the wedding and all family around and I played at my level, so pretty beginner, but with confidence and, according to people, in a lovely mood (not my words!
I played mostly pop music, and 95% English language songs, from 70s to 90s, so German people also knew them. From Beatles to Abba, some David Bowie and such. My playing was using chord and lyrics sheet music (what you would use to play guitar) so the melody was platyed by ear. I use to play a lot like that at home, and it paid off. I tried to break chords, add bass when possible, use different rithms... Basic things but, well, it is what I can do now.
My wife was sitting about 5 meters from the piano, chatting with other people, and she said it was an enjoyable experience. I was like floating after that improvised performance.
After the dinner, there was a music group (percussion, bass, keyboard and singer) who played from 22:00 to about 0:30. Due to restrictions, we should end celebration at 01:00, so I was unable to play then, which is when I intended to do it. So, if I had not played before, I would not been able to do it!
So the moral of the story is: take things as they come, don't hesitate to play in public and enjoy music!
For me, it has been the first time I have played with more that 3-4 person around, and also with completely unknown public among them. And I enjoyed every minute