Next time, perhaps implement only one of the already existing methods and then the newly proposed idea. If the litmus test is that your new idea outperforms all of the baselines, you can test that already early on.
In general, incrementality is key: if you're looking at a task that is going to take you 10 month to realize you need to be aware of the risk you're taking. Be prepared that the results may not end up being what you hope for, or, if you cannot take that risk, find an alternative way of moving forward. Good planning is a valuable skill to have.
For now, would it be possible to analyse in depth why the new method fell short? Is there perhaps a certain sub-problem that it does very well on, in which case you could still extract a (somewhat weaker but) positive result?
Minimally, I'm sure you gained some new insights, and perhaps are even in a position now where you can correct some misconceptions you might have had about your problem: the outcome of your experiment is that something inherent in your problem is not like you thought it was, or else your method would have worked. So you may ask yourself what is it that's different?
If an unexpected obstacle drops on your path, don't just stop. Look for a way around it, or a new direction altogether.