Did you oval the pipe when unrolling it?

You may need to get a flaring tool and use it to make the pipe round again.

Simply clamping it in the flaring tool usually rounds it out.

Are the couplings generic or name brand? It seems like the friendly neighborhood box-store sold you some inferior plumbing parts. No surprise here, I can't even find the necessary parts, at that place, to do ANY plumbing job!

I only buy plumbing parts from places that are organized and completely stocked. The HD should not even carry plumbing, IMO.

Per ASTM standards all outside diameter of Copper Pipe, both hard drawn (rigid) & Annealed (roll copper pipe) are made to the exact same size standards whether it is name brand or generic.

The outside diameter remains constant and the difference in wall thickness is made up on the inside diameter.

By example:
1/2" copper pipe both rigid & roll has an OD of 0.625".

type K ID is 0.527"
type L ID is 0.545"
type M ID is 0.569"

ASTM allows a slight tolerance on the ID (female opening) of fittings

by example:
for 1/2" fittings the ID of the fitting may be a maximum of 0.631" and a minimum of 0.627".

From my experience the couplings are usually the tightest and sometimes difficult to fit on the pipe, but they will fit however with only 0.002" difference they can be difficult unless the pipe is perfectly round and both the pipe & fittings have been properly deburred and cleaned prior to fitting.

Great care should be taken when handling copper pipe. Simply dropping a length of a concrete floor can be enough force to knock the end of the pipe out of round, making fitting a joint nearly impossible.

Copper pipe should only be cut with a good quality tubing cutter that is properly used. The tension should be increased as the cutter is rotated around the pipe. Simply placing the cutter on the pipe, cranking down the tension then rotating the cutter is enough to force the pipe wall out of round and seriously damage the cutter wheel on your cutter. (Those cheap little red mini cutters are at best useless)

Under no circumstances should a hack saw ever be used to cut copper unless you are tearing out old work and planning to dispose of the copper.

If you have a lot of fittings to clean here is a trick. Get on of the cheap wire fitting brushes with the simple wire loop handle and cut the handle off the shaft, then chuch the shaft of the brush in your cordless drill. You can then perfectly clean the ID of a fitting in a couple seconds.

Did the couplings say "Made in China" anywhere on the package?
I'd think Nibco to have tighter tolerance.
For soft solders to work properly, assuming the joint is clean and fluxed, the clearance need be at least .002" and less then about .007".
I haven't seen much quality pipe or fittings made in China.

Something was definitely wrong with that particular Nibco bag. Pipe was cleaned, deburred, round (I clip off an end from new pipe to avoid dings) etc. I bought some from a plumbing supply and also my local contractor supply and those were fine.

BTW, were you ever repairing a pipe, with phone ringing, dog barking, kid crying, etc. only to end up accidentally cutting the adjacent (perfectly fine) pipe right next to it? That about sums up my Friday afternoon. Grrr.