And it's a pretty stamp, so do please show us more!

The reason your pics are coming out so small - at least the last one - looks like you are not cutting off the white background (cropping). You can do this on your computer or use the website tools.
To do it on your computer, try double clicking on the image after you have scanned it and saved it. When it opens, if you are lucky like I was when I learned this a few weeks ago, the stamp will open up in a program that will allow you to crop off all the background (leave the perfs in the picture though).
Then you save it and use the file name to load it here again.
Good luck - hope to see your pics soon.