You can enter again with the help of the fairy from the park, unless you did not buy the amulet and hide it near goth-girl, then you would need to start over.
I bought the amulet and hide it near the goth girl the problem is I forgot to buy the gold coin to start the fairy quest and then got locked out of the store
After you have hidden the amulet, there schould be something new for sale called "mysterious vial" or something like that, 4 vials in total with 500$ each, one of them is used to spike the drink of the goth
