Just like what Akamine-sensei relayed to Hajime, Megumi's group was actually by Ueno Park, enjoying the sights over there before they go to Ameyoko for a quick stop so they could buy some souvenirs. They figured that they won't have time to do such a thing while they were on a trip tomorrow and by the last day, they concluded that they'd just enjoy themselves.
Getting souvenirs is pretty much an errand that the three of them want to finish as soon as possible so they allotted a portion of their time that afternoon to check it out. With this, they won't have to worry about running out of time throughout the school trip. Cramming most of their so-called 'errand' in every free time they had was the optimal decision— or so that's what they decided amongst themselves.
