Didn’t you give measurements when placing order (as in inches - instead of saying it should be long enough to touch the border on the skirt?) I think to avoid confusion its best to provide measurements that way but anyway, what’s done is done.
An additional border seems to be the only option if you want to extend the length of the shirt and depending on the type of work you have you on your existing border, you can use two strips of 3 inch work or a 2 inch with a four inch. If your existing border is a sort of repeat pattern then get additional fabric patched and get similar kaam done on that. If you can post the picture of the border only, some one here must be able to suggest you some options.