The M235i has been out long enough to show that it has been a fairly reliable car.
Consumer Reports rated the 2016 model as having a potential issues with "Power Equipment". Which is what they use to describe: "Cruise control, clock, warning lights, body control module, keyless entry, wiper motor or washer, tire pressure monitor, interior or exterior lights, horn, gauges, 12V power plug, USB port, alarm or security system, remote engine start, heated or cooled seats."
If issues in this area have already been addressed in the past, you should be fine not needing to pay for this expense. Otherwise, it's up to you to decide if any repairs in the above-mentioned areas will cost more than the $3500 you paid. Personally, I've never believed in any kind of extended warranty programs.