Recently the question came up about what to do when your Saint Birgitta's Cap strap (the loop) is too long. In this video, I present two simple solutions that you can use until you decide it's time to shorten the strap permanently.
I personally recommend that you use either or both of these techniques for as long as they work. It's always better to have length, since your hair will grow and change the fit of the cap as it does. You may find, when your hair is longer, if fits correctly again. Laundering will also affect the size. If, however, you're consistently having tension issues regardless of your hair's length, that's an ideal case in which cutting it down is the way to go. Try timing that change so that you're establishing your new strap length when your hair is the longest you're likely to let it get, and make sure that the cap has been thoroughly washed and dried to ensure that it's already as small as it will be.
If you're curious about making your own cap, check out my information, or head on over to Larsdatter.com for links to many more examples.