Where did the floatation collar and sea anchor attach to the command module?

Work in progress!

There was no set of three or more attachment points.

Only a single attachment point below the hatch was needed to fix the sea anchor and both ends of the floatation collar, the sea anchor ring.

Apollo 17 after recovery aboard the Ticonderoga, image S72-55886 from ALSJ. The sea anchor ring is inside the red circle (annotated by me) below the crew hatch.

The sea anchor was attached to the ring by the first rescue diver.

_{Image source: http://www.collectspace.com/review/apollo-recovery-operational-procedures.pdf}

Swimmer A fixes the red striped left end of the collar to the sea anchor ring.

After inflation the collar is secured with two vertical straps on the rear side of the CM. But these straps do not take the buoyant forces of the collar.

An image of the Apollo 11 flotation collar drying after recovery:

_{Image source: https://www.nhahistoricalsociety.org/index.php/apollo-11-mission-and-recovery/}

All the ropes attaching the collar to the Apollo capsule are to be seen. The upper rope ring above the water is marked with green arrows. The lower rope ring below the water and the CM heat shield is marked with blue arrows.

Note the red (port side, left) and green (starboard side, right) stripes on the floatation collar. The bow of this ocean going vessel is at the top of the image, the stern at the bottom. See Wikipedia.

The attachment point is directly under the door:

^{_{Image sourced from Smithsonian: https://airandspace.si.edu/collection-objects/apollo-11-flotation-collar/nasm_A19780202000}}

Because of the conical shape:

_{^{Image Source: https://twitter.com/apollo_50th/status/1154117320047861760}}

no other point is needed:

_{^{Image Source: https://www.flickr.com/photos/brostad/3548675310/}}

Once laid around and fastened, you do not need to fix it more often.