An interesting question. My take on it is as follows.
There are dozens of metaphors of various kinds.
There is an obvious overall metaphor of the 'show' representing life, particularly the singer's life. 'The show must go on' = 'life must go on'. When one considers how Freddie Mercury's life was so closely entangled with show business, one could argue that in his case it is barely a metaphor at all! Go here to find out more about what a metaphor is.
There are then metaphors that follow and support the inherent logic of the 'show' metaphor (the curtain, make-up, top the bill, holding the line, etc).
As well as the overall 'show' metaphor, there are others not particularly related to shows that he uses to make certain points. One example is
"Outside the dawn is breaking
But inside in the dark I’m aching to be free"
while others, for me, strain the relevance to shows:
"My soul is painted like the wings of butterflies
... I can fly"
Some of the metaphors I found hard to understand or just didn't work for me. For example:
"Fairytales of yesterday will grow but never die"
seems odd as I don't think of fairy-tales as having life int he first place or that they might 'grow but never die'. Thinking about it though, it does maybe fit with the show going on, as if he's saying that this life is like a fairy-tale started long ago and which continues to have bits added to it. I suppose a lot of pantomimes are fairy-tales, aren't they? Still it seems somehow out-of-place and unsatisfactory where it is. I wonder if that line is where it is because it rhymes!
There are alsoother more universal metaphors, like inside/outside and looking for/finding and lots and lots of metaphors of the kind that are so universally used that we hardly notice that they are metaphors at all. Like:
"I’ll soon be turning round the corner now"
"...to carry on"
"I’ll leave it all to chance"
"I guess we know the score"
"overkill"
What does it all mean? Ah well, the song itself asks that!
Hope that helps.
Phil Swallow