There are only two bad ends (if I remember correctly).
Just make sure to save before choices and pick the other option after loading. It's coded so that the specific choice right before the bad end is what leads it to the bad end, so the choices before those aren't the cause for the bad end. Early choices still do affect some dialogue later down the line.
There is one missable CG/scene if you pick the wrong choices early on. The CG gallery (clicking the missed CG slot) will give you a clue on what choices you missed.
I hope this helps ^^"