Success to complete the event will be determined by
Given the time constraints you will not be able to add greatly to your fitness base (1). This leaves you with Strategy (2) and execution (3) as factors you can optimize to give you the best chance at success.
Strategy looks at things such as pacing during the event, knowing how/when you will eat and during during the event. Strategy can also include things such as getting sufficient rest prior to the event so you can be at your best.
You can have the best strategy in the world, but fail miserably at executing it. For example, you can plan to eat every 45 minutes, but when actually riding endorphins can kick in making you think you are more on top of things than you actually are. This could make you feel like you skip eating when you planned which can have consequences later in the event.
What you can do in the time left.
Go on at least one very long ride (e.g., 4-6 hours) at least 1-2 weeks before the event. This will give you a feel for what you will be up against when you do your 220 km. Practice eating, drinking. If you sufficiently stay on top of these you shouldn't feel thirsty or experience bonking. That said if you experience either you will need to improve your execution of these. The 1-2 week buffer will give you time to recover before your big day.