Maybe you will have more luck on the 'other' flat earth forum. This one banned a few flat earth gurus who would have been able to answer your questions. Look for a member named İntikam. That guy is a legend
Both sites are run by controlled opposition though although I would say the genuine believers have gravitated over the other one. Just watch as I get warned or banned for speaking the truth.
As to my answer to your question, given we know so little about the universe and the nature of well anything, I have a more agnostic approach.
For example, there are theories (and these all came from well known scientific geeks) that our universe could be a holographic projection and that the '3 spatial dimensions' is merely a matter of perspective.
Or that it could be 10 spatial dimensions. We only occupy 3 so we cant fathom or comprehend anything greater anymore than a 2D flatlander could comprehend or view our 3D world. Those 'virtual' particles that seemingly 'pop' in and out of existence in defiance of the laws of physics? Well they may be occupying other spatial dimensions we aren't a part of and we only see flashes on their existence as they move around.
The shape of everything is also dependant on the speed you are travelling. If you were to hitch a ride on a photon, the start and finish lines of the ends of the universe would be on top of each other. Pretty flat
We could be in a matrix. Therefore our universe is rendered into nothing more than ones and zeros. Who's to say the programmers couldn't make an exception for what the shape of this planet is?
We could be a simulated universe. If we end up with the technology to create simulations so realistic that we could create a universe of people that believe everything is real, there is an infinitesimal chance that our universe is the 'real' one. There could be an infinite amount of simulated universe. Simulations within simulations for infinity. We may be in one of those. When mankind reaches 'the singularity', there is no limit to our technological potential.
Point is, I prefer not to settle on an answer without absolute proof. Unfortunately to satisfy me, that requires a complete understanding of the universe. An unlikely feat in my lifetime and perhaps beyond the reach of any human, ever.