Having an issue with image import in pop up plugin

Hi

I installed pop up plugin and the process of running the plugin is fine. However I am using a simple image that I created in Photoshop. The size of the image is 511 x 311 pixels at 100 dpi.

the image is clean, the text is sharp.

when i import the image into the pop up it automatically resizes to a smaller image 300x182 pixels.

the settings for the size of the pop up window is also set to 511 x 311.

the problem is the image appears off centre and fuzzy.

Any ideas why and how do I maintain the size of the original image.

I also adjusted the code in the html

<img src="http://domain.com/cp/wp-content/uploads/2013/04/millionaireblueprint-300x182.jpg" alt="blueprint" width="511" height="311" class="aligncenter size-large wp-image-399" />

any advice ould be fantastic.