Welcome to the wonderful world of machine embroidery (ME) and AnnTheGran (ATG). ME is the most fun craft, it is beautiful, and creative, you are going to fall in love!
ME and the borders available are not digitized to be stretchable. You probably needed some stretch for your task. One never knows if someone has determined how to do stretchable designs, but to my knowledge, there is no way to do it.
However, I applaud you for trying something out. Some users are hesitant to give things a try, and that is sad because, with a little knowledge, we all must get in there and try something new! Frankly, we are all learning, even those of us who are veterans of ME learn something most every day.
If you can, we could use a photo of your top to help with any issues. Just FYI, tear away stabilizer is probably not the best for this application. Because of the lack of stretch, you would normally use an adhesive water soluble stabilizer. ATG has a great one and is reasonably priced, especially if you join her Club.
Do check out my forum post for the PE700II which is about a Brother machine, but the steps and information apply to any machine, give that a read. I also have a Blog Post about What I Wish I Had Known when I began ME.
So, ask a lot of questions, read, read and then enjoy your machine. You might want to start off with something that you don't wear any more and frankly, you might find new life in the garment with your beautiful new craft!
Pat, The Avid Embroiderer
If you are interested in selling your projects, you can determine your costs and profits quickly with my Spreadsheet.
If you want a lot of great information on working easier, faster and more confidently on your computer, check out my Tips and Tricks.
If you want to see my pashminas (that I successfully sell retail) check them out here. I also wholesale them.