I'm decorating my second cake. And I don't have enough fondant left to make a border around the bottom of the cake. What can I do? Would it look alright if I piped some buttercream frosting for the bottom border?
Yes it will be o.k.
That would look just fine, I've seen all sorts of cakes done like that. Another alternate would be to use a fabric ribbon.
Yes it will look ok. Royal Icing will work fine too.