AI have accidently used self rasing flour in my fruit christmas cake instead of plain flour, will it taste different, should i throw it out and start again?

I think it will just raise a lot more when baking. I would bake it and see how it comes out. I'm guessing your Christmas cake is like a fruit cake here in the US. It will come out fluffy, not so dense. 

AIt looks normal when it came out just a bit softer, yeah our christmas cake (in uk) is a rich fruit cake