Barney states he's been on the force for a year and a half. This doesn't fit with the first episode, "The New Housekeeper," in which it appears to be his first week on the job. This discrepancy will bear out five years later in "Barney's Physical" when he gets a party celebrating his fifth year as deputy.
At Walker's Drugstore, when Ellie walks over to Andy to flirt with him, a sign is visible on the wall with the misspelled word "Enlargments."
At the beginning and end of the episode, Andy and Ellie talk about going to a picnic. However, during the bulk of the show they refer to a dance.
There may not be a plot hole by talking about the picnic and the dance. In small towns, they could be having a dance at the picnic. Could have lots of things like cake walks, and even some carnival games.