Am I infringing on a copyright?

[Sevenclarks]

Over a year ago I purchased a pattern for modest swimsuits to sew for my daughters. The seller lives in Canada. I am a work-at-home-mom, a seamstress, and I love the suits so this spring I made up several and sold them. Someone pointed out to me that the patterns had a copyright, so I made changes to the pattern (neckline, waistline, sleeve length, skirt width, etc.) and carried on. I did some research online and found many, many patterns for modest swimsuits, some almost exactly like the pattern I have.
Now the woman that sold me the pattern is claiming that I'm infringing on her copyright. I emailed her back and explained that I was using a pattern on my own design, similar to hers (and several others) but not exactly. She wrote back and said if I don't quit immediately she will have her lawyer contacting me. Yikes!
I did some research on copyright law and I thought I fell into the "useful items" category, but maybe I don't. Can anyone help me? I certainly don't want to be doing anything wrong, but it seems like there is a lot of grey area here.
Thank you so much for any wisdom...

 

[seniorjudge]

Do you really think some Canadian would come to the US to sue you?

What do you think her damages would be?

I wouldn't worry.

 

[Sevenclarks]

So what is involved in stopping someone you think is infringeing on your copyright? Would she have to physically come to where I am?
What type of damages are involved in settleing a suit? What are they based on?
Sorry for all the questions, but I'm not very knowledgeable about this. Thanks!