You will not make it rise too much if you add more self-rising flour. I would lower the amount of sugar, and if you have time, see hoe just that comes out. If you still feel it needs more flour, then you can make another one and lower the sugar and add more flour.
However, I wouldn't add to much more flour or it will overpower the sweetness of the cake. You could also use a combination of self-rising flour and all-purpose flour if you are worried it might rise too much.
I have a great recipe for a 4-layered chocolate pie if you wanna try it.
It is simple and easy.