Smooth rough edge of rectangle

[dianagrasshopper]

I've edited the edge of a rectangle shape and that edge is blurry now. How can I fix it? The rounded edge looks fuzzy or rough now. 

[JJMack]

There is no shape layer in your psd file???

[dianagrasshopper]

Hi JJMack. Pardon my confusion. Isn't Rectangle 1 a shape layer? 

[dianagrasshopper]

JJMack. Please take a look at the Shape file. I accidently uploaded the wrong file originally. 

[JJMack]

It does not matter. Its more to do with the number of pixels,   You are not going to have a small 216 pixels wide images the will has a small shape with a smooth shart curve  edge. There are too few pixels for that.  Here I made as shape in the test PSD you poster   I zoomed  in so you can see the curve edge large.  I them  resized the document to have a 2000 pixels wide canvas size and zoomed out so you can see the curver small.