Editing a scanned drawing's colors using shaped color fills and transparancies

Hi,

I am a new user of Xara Photo and Graphic Deisgner 13. I am attempting to edit a scanned abstract drawing where many of the colors are similar, resulting in them printing as all the same shade of red. I am attempting to change some of the reds to have a greater degree of shading. I am aware that I can probably do this using masks and RGB tweaking; but it occured to me that I can also use a drawn shape and color fill with transparency to change the shade. This worked very well; but it caused one problem I don't know how to solve.

The image I am editing is intended to be uploaded to a website named Zazzle that takes your artwork and puts it on their products. This includes anything from notecards to canvases, to clothing, to shoes, etc., etc. Customers browse the site to find products and images they like. I also have a free webpage on the site where I can promote the sale of these items with my artwork on them.

The image must be a high resolution preferably png file which can be resized greatly for the canvases or left as is for notecards and the like.

While experimenting with the size of my image, I discovered that the edits I performed stay the same size while the rest of the image increases. Is it possible to make the edited shapes part of the scanned image so they will increase and decrease with the rest of the image?

Thank you for any help you can provide!