Yes it only is fertile if there is a rooster it would help also if you could send a picture of the egg. This is my hens fertile egg. So if your hen lays a egg like this that mean for sure you have a rooster.
X2 however there will be a circle but it has to be a bullseye to actually show that it is fertilized, store bought ones are about 45 days old when they hit the store so you can't see the circle any more.
What is that gray hen you have she is a BEAUTY!!!