First of all, nice to meet you and have a great time here on PhotoBlog!
As for your question - were the images you are trying to upload scaled down to smaller dimensions? “500px wide” should just mean that your photo width is smaller than this mentioned 500px. Unless you or the software you are using changed the dimensions of the image, it should be much bigger than than. For example iPhone 7 or Samsung Galaxy S7 have camera with 12Mpix resolution, which translates to dimensions of 4032x3024 px (width and height). Most of current cameras should have at least that resolution.
That is why I suspect that maybe PB have some trouble with recognizing your files or maybe with their format (are they in JPG format?)
If you can, please post more info and we will figure it out