What do you mean by "terrible"? Can you illustrate what you mean with screenshots?
If you draw an image at 64x64 and scale it up, there is no more detail to show, so you'll see linear or point filtering in between pixels. Because of this, often it's a good idea to draw your artwork at a higher resolution than necessary - e.g. draw a 128x128 image, then size it 64x64 in Construct 2. Then when the screen scales up, instead of just blurring or pixellating it, it will gradually show more detail, which is quite a nice effect.