Yes, you can always end your Stack early and retrieve your funds! Simply go into your Stack, scroll to the bottom, and click Withdraw! You will then be taken to a screen which shows how much you have in your Stack, therefore how much you will be withdrawing. Click next and “Yes, cancel” on the pop up message if you want to cancel your reoccurring payments within that Stack (hence ending it early).
You can also delete a Stack! Frist, do the steps above to retrieve your funds. Then, go into your Stack, click Edit in the top right corner, scroll down, and click Delete. Confirm you want to cancel remaining payments, and now your Stack is deleted and will not show up on your feed or personal profile!