In my experience, it might close up if the water parameters are not acceptable or the flow is too strong. from what I can see, this looks like it just found a spot it prefers. These creatures will move around until they find a good spot they like. If you'd like to share some water parameters and more details, it might be helpful.
Anemones are very delicate creatures and need pristine water conditions to thrive. Not saying it can't be done in a new system, but this why we typically recommend waiting on anemones for at least a year. This way the tank has a chance to stabilize, and you as a young reefer know what to do, and look for if things start going south.
3 days really isn't a long time for a nem imo. It may still be acclimation to your parameters. You can help it by keeping your water stable as possible so the nem can get to the finish line without it being moved/reset along the way... So to speak