Normally it would be OK to do whatever, it's your picture, you are its sole owner and master. If there is something you can be sure to be able to rule upon on your life, it's your pictures.

For photojournalism that would already be a wrong practice. But I suppose this was not a photojournalistic image.

If the picture is made for the "consumption" of people attending the event (a marriage?) and local to your church, then flipping the image might cause a sense of "innatural" because you also flip the architectural features - bell tower to the left coming from the bridge, instead of to the right - and the orientation - sun coming from the opposite direction it normally comes.

If the boy had been framed on its own, no problem. Framed as it is, if you hang it to your wall everybody seeing it will tell you that the sides are reversed...