Does the animation itself last exactly 3 seconds? If so you can go into the animation 'edit' view and tweak some settings there.
1. From the layout view, double click your sprite
2. Select the animation itself from the list on the right on the right,
3. On the left side there will be some options. You can set it to 'loop' and set the 'repeat to' as the frame you want it to loop from.
Maybe this will solve it?