When Bilbo sees the mountain, it unnerves him.
Bilbo had come far and through many adventures to see it, and now he did not like the look of it in the least. (ch 10)
The landscape has changed a lot lately, even to Gandalf who has seen it recently. The roads have fallen into disrepair and the creeks have swelled. There have been floods and earthquakes. These are likely Sauron’s influence. Bilbo, on the top of the barrels, “had come in the end by the only road that was any good” (ch 10). It is not a comfortable one.
[He] did not like the way the Mountain seemed to frown at him and threaten him as it drew ever nearer. (ch 10)
Bilbo is hungry and has a cold, and the Mountain seems threatening instead of fun. Bilbo’s thoughts foreshadow the trouble ahead, both in terms of the dragon and the war that follows. He is right to be worried!