UPDATE (and a few questions):
~3hrs digging in all 6 side towers (DONE)
~4hrs locating, picking up, and dumping 2 tons of Masonry sand (also called fine sand... at least in the Seattle-Redmond area).
~.5hr rolling out wall... but it was 6 inches short!
~2h manually scrunching up small spaces out of the curved section bottom rails... 2 inches were honest gaps, but 4 inches we had to go over the stop bumps in the cuffs (cheating). We tried our best to distribute these on both sides of the round and even took wall apart twice to suck up 2 inches from the far circle. Ugh... I hope this doesn't screw us over when we install the top rails.
2hrs preparing sand including shoveling, grading, checking height with laser level, adjusting, tamping, and brushing (right before laying down happybottom 1/4" foam bottom).
.75hr installing foam coving (no problems) and Happybottom. Note the happybottom roll was barely wide enough to cover width of pool... Pool salesperson told me it would be single folded sheet. Duct tape and extra time seem to be an OK solution (but would have preferred nice wide single blanket.
.5hr Pulling liner over pool and instaling V-bead most the way around.
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=12.75hrs constructing walls and nearly ready to stretch liner for water.

NEXT: Finish liner installation, then start filling!
Today It was 8PM and temp was dropping from ~75 earlier to mid-60's by the time we got the liner in (and ~2' crooked). I lost my nice pre-warmed liner install window, so I'll wait for tomorrow which should also be good. (I pray our two adventurous cats don't jump in to check out the fishy liner, then use their claws to climb back out.)

QUESTIONS:
1. How concerned should I be about having to suck in 4" from curved areas to make the wall connect?
I'm concerned the liner bottom seam or top rail will not connect properly due to the several 1/2" shortened sections this created. I still haven't figured out how we screwed up to make wall 4" short. My only guess is the side towers might be a little more than 12' wide. (I counted on the strap and diagonal measurements when squaring... I assumed the bottom straps would force columns to be 12' wide.)

2. How do I clamp the liner up so I can use the water-stretch technique?
I have 50 clothespins, but they are cheap plastic ones and there's no way they can hold any significant weight.
Do I need to buy a bunch of clamps (with soft/rubberized tips)? (that's my guess)
If yes how many for 12'x24' oval?
Do I just leave V-Bead installed then hike up the liner and temporarily hold it with clamps?
Note I installed the V-Bead almost all the way around just to hold the liner overnight (and help warm it tomorrow morning before I start install around noon-1PM)

That's it. I got some time-lapse video of this stage of construction. We also got a new 8 week old puppy. He loves sand, getting under foot, and pooping right where we decided to build the ladder (ewww!).

I am SOOO looking forward to having a filled pool by 4th of July (friends&family can enjoy it while I install basic or ad-hoc plumbing and check chemical balance). Sometimes I really enjoy this project and the deep senes of satisfaction. However many times I've felt like my time would have been better spent working for a better bonus or spending more time focusing on family. Good news is the entire family is very supportive. We have built some good memories along the way. I choose to stay positive overall... as long as the results turn out well.