Light the candle and say:

"Gods and goddesses of nature, I ask of you a request small.
Like a stag, I wish for antlers.
[Size, small, large or medium] sized [colour] antlers right on my head for all to see.
I wish for this and this alone. This is my will, so must it be."

After a few days, they should start to grow in, but you may need to will them in. If they don't grow after a month, then try the spell again.

****COLOURS THAT AREN'T NATURAL WILL NOT WORK! DO NOT PICK BLUE, PINK, PURPLE, OR ANY COLOUR THAT YOU WOULD NOT SEE ON A STAG****