First, please don't say that you are stupid!! You are learning and you will need guidance. I hope whatever I told you is helpful for you, since I have been in business for a while, so these are kind of easy for me, but in real, the implementation is hard some times......
Anyway, back to your case. You are correct. Although your case is just a case, this bank does not excist, but you still have to treat it as a real bank in the real life situaion, then PEST will work. As far as I can see, all your ponts are valid, but there are more into it. Not just the ones that you listed, but there are more...
In the Political point, remember what I told you. This is a big bank and it's been in business for a while, so which means, they will have political connections. Now if this bank decide to change, will it effect any of that?? Also, this is just external. How about the Internal political point? What will all the CEO do, if they have to make changes. What about the managments?? Think of these and be creative!
In the Social point, birth rate is decreasing, correct, this is also external, what about internal??? Will they get new people that has experience to come into the bank and keep the bank competitive??
In the Economic stand point, if the changes are in place, will there be any salary changes for all the personnel?? With the new IS department, what will happen with the people that is working now? Remember, there is a possiablity for the bank to down size, so what kind of effect will it have?
In the Technology part, you are only talking about the internal thing like the transaction will be faster, but will it effect the personnel right now? Will they need more people or les people to do the job? With the changing technology world, will the bank need to keep upgrading their IS? This will be the external effects.