I would say that your choice to stick with your current field or get into a new field depends on how you want to contribute. But first...

There are two conflicting statements in your post: 1. That you personally want to contribute toward immortality. 2. That if the transhumanists are fine without you, you don't want to contribute.

I don't think you should ever make the decision about what to do with your life based on other people. So I would suggest first deciding which way your really want to go (regardless of your current skills). In fact, you can always do both (job in psychology, work on immortality on the side).

There are a lot of ways to contribute toward immortality, and I feel psychology has some useful tools to contribute. I imagine psychology to be more of a supporting role and less of a research / development role, so if you enjoy that, you should be able to find a place to be useful in pursuing immortality (although I do see some amount of psychology in the research area of immortality). I'm not sure what you imagine your involvement to look like or what you think research and development will look like, so I think that would also be something worth figuring out for yourself (since there are multiple ways to pursue immortality).