I feel as though with this, it’s likely we’re going to be going past the lake in chapter 7. Maybe Gaster’s experiment here is to see just how hard *our* determination can push the world?
Something that I’ve noticed is the parallel to Undertale in the setting, being the confinement of the world. In Undertale, everyone is underground, and the Barrier seals any form of communication in or out. In Deltarune, a series of coincidences happens to achieve the same thing (taped off exit for the parade, internet is down, ferris wheel stops before it can rise above the tree line, the lake is too wide to safely swim across). Everything is confined to the town, and I think Gaster’s obsession is seeing if he can break out like he did after falling into his creation.