... is there a trick to getting them to close?
I have the Like 200i and believe the foot pedals are identical to the 150. I select a round button to spring the pedal out to the open position. They are held open by the tension of the spring and the weight of the foot when rested on them. They are not locked into the open position, so to close them, I just push them back into the body where they are caught (and held closed) by a latch(?) in the assembly.
It is worth noting that some owners replace original foot pedals for the comfort of their passenger.
So, your inability to close them (especially on both sides) means they've been tampered with or the latches are both broke - which seems to go against a known failure rate.