This is a great question with more than one possible answer.

A very good discussion about the curvature of the universe is available in

https://www.researchgate.net/post/How_do_cosmologists_determine_the_curvature_of_the_universe_based_on_astronomical_data

and

https://www.researchgate.net/post/The_flatness_problem_or_why_do_we_think_the_observable_universe_is_big

https://www.researchgate.net/post/Could_the_universe_be_a_non-orientable_manifold

More to the point, locally the universe appears to be approximately flat.   This issue is discussed in

https://www.researchgate.net/post/Could_the_universe_be_a_non-orientable_manifold

and a new model of the universe that considers the flat FriedmannLemaître

model is given in

https://arxiv.org/ftp/arxiv/papers/0801/0801.0552.pdf

Dear prof. James F Peters:

Thanks  for  your comments. You have always interesting and full of surprises data.

With best

reza