Please HELP. Trouble with Eurail Seat Reservations

This is my first time purchasing a Eurail Pass and first time traveling to Europe.

I need to train across borders several times and my trip begins in 2 weeks.

I should have done this research sooner however I feel I was mislead to believe that Eurail is as simple and efficient as they make it out to be. Long story short 3 different train routes which I need to take because of previously made arrangements are showing up “sold out” of seat reservations via both Eurail and the linked train sites.

What do I do? Is it true you can board without a seat reservation even though it claims to be required? I’m traveling from Antwerp>Paris, Paris>Antwerp, Antwerp>Lyon, Lyon>Alba or Piedmont region.