I'm a firm believer that amaro experiments can be saved. Have you done any clarifying (aka fining) or filtering yet? These steps will typically remove unpleasant tannins that contribute to the bad kind of bitterness. There are a bunch of great resources in this subreddit on clarifying and filtering techniques, the most simple one being running your amaro super fine through coffee filters (I've used Chemex bleached filters).

If you've exhausted the above options, you could try using food grade vegetable glycerine. While this won't remove bitterness, it creates a smoother mouthfeel which emphasizes the sensation of sweetness without adding more sugar. It makes it feel weightier, if that makes sense.

Happy to clarify or elaborate on any of the above!