Most places I’ve ordered blinds for will allow you to reorder a different measurement, up to a lifetime cap (like 4 times per person/household - you only get to fuck up for free so many times). The one I messed up they just let me keep because it was a custom size (still in my garage for some reason)

It’s a pain but it is the way to go if you want your blinds to really be good for the space.

Only time I’ve been annoyed was a cloth roller blind I ordered to cover a large door window that I measured perfectly but nowhere in the description did it say that there was a 1/8 gap at each edge and the overall width of the blind was 1/4" shy of your measurement. Returned that one and just got a bigger one where the blind was the actual width I wanted…