All networks are different and follow different rules when it comes to images sizes. If you have posted to Instagram with Blog2Social and your image is not displayed the way you wanted it to or not at all, the size of your image could be the reason.
Please also make sure that your image is in ".png" or ".jpg" format since these are the formats which are supported by Instagram.
Overview of the images sizes suitable for Instagram
Although Blog2Social adapts your blog's images to the respective networks you are posting them to, images that are too large or too small will result in, either not being posted at all or appearing pixeled as Blog2Social tries to fill the images frame in the network.