Hi, please mind that this cut is often parted to the side, but those with a long forehead may want to wear a bang to downplay that feature. If you have a square jawline, you should have a length that exceeds below it so it balances that portion out. Your stylist can help you determine the best length and parts for you and your hair type. So, read carefully about undercut haircut https://lovehairstyles.com/best-undercut...yle-women/
Hair typically grows about a half an inch a month. So it depends on your endgame result as to what do do with it.
You can leave the top to cover the sides as they grow out. Or you can trim the top a little or a lot. Just be patient and get a strong gel line got2be glued to hold your hair while it grows.