Yes, you can cancel your Tickertape Pro membership anytime you like. You will still continue to enjoy all Premium benefits till the remainder period of your subscription, after which you will go back to Tickertape Basic.
After cancellation you will only have your first 3 saved screens in your library, and will lose access to all other screens saved by you. Also, if you have any saved screens with Premium filters, you will not be able to load them too.
Please Note: Cancellation is only available for the monthly subscription, since all other plans are non-recurring plans they are non-cancellable.
Please visit this article to know how to cancel your Pro membership.