Hi Kieran - hard to tell from the picture but it looks like there may be a little bit of life left in your tree, and let's face it you've got nothing to lose by trying to save it!
First of all, carefully invert the tree and gently "comb" through the foliage with your fingers to remove the dead leaves, which will allow you to assess what condition the rest of the tree is in. (The foliage looks a little over-dense anyway, and in the future it would look more like a tree if it was thinned out, giving sight of the trunk and branches).
Some of the most misleading advice given to newcomers is to let the soil dry out before watering - when it gets too dry it can become impervious to water. So, when you do water it the very top of the soil feels wet, but no water permeates down to the roots where it is needed. Take the tree and place it in a bowl of room temperature water for 10 - 15 minutes, immersing the whole of the pot (you may see air bubbles rising from the soil if it had dried out completely) In the future don't let the soil get less than "touch damp".
Also - another misleading statement is calling a bonsai tree an "inside" bonsai - very few trees flourish to their full potential inside unless you have a nice sunny windowsill (or even better - well ventilated conservatory)
Good luck!
