It is impossible. You never get to be on top of everything. Since there is always shit that needs to be done. It is often called the productivity myth. More discipline or a better system won’t lead to less work and less stress. Since new things just keep coming.
You just need to accept that life is like this and that it’s completely impossible to forever finish your todos. So therefore you should just schedule down time and don’t feel guilty that you still need to finish things since it is a never ending stream of things to do anyway. Just prioritize the most important things.