loss of detail

Hi, I am new here so forgive me if my question is silly. As a GM I want to upload my map to use it. It's a Jpeg file, 3508 x 4960 pixel (I printed it on a A3 sheet) and with lots of details. I upload it (2MB like the original) and I drag&drop it on the Map Sheet. That's the result. As I try to enlarge it to make it full page, it loses resolution, like this What did I do wrong? Please help! Thank you in advance :)

I think there is a memory limit per image loaded.  If you can break your map into two, or maybe four, sections, and load them individually, it may solve the problem.

2MB seems small for an image that size.  Are you certain you're uploading a full-resolution image? Note:  Since it's a map, and uses a limited color palette, that file size might be possible.  Just unlikely.

Make sure you are not stretching it too large on your map layer. You can right click on the image and under Advanced choose Set Dimensions, and you can apply the exact dimensions of the file. If you tried any type of automated align to grid it could have blown the image up significantly, causing the blurriness. Sometimes it also take a while for an image to load - although a 2MB file doesn't sound that large to me, it could still be trying to load it and is displaying a lower-res preview while it loads in the full file.