The word “ठीक” means “good”, “correct”, “right”, etc. It is an adjective with various uses.
One idiom involving ठीक is very similar to one usage of “just” or “right” in English:
लड़के पेड़ के ठीक पास बैठे हुए हैं – “The boys are sitting right next to the tree”
मेरा घर नदी के ठीक उस पार स्थित है – “My house is located just across the river”
ठीक दो दिन पहले मैं वहां गया था – “I had gone there just two days earlier”
Notice the location of ठीक in compound postpositions.
This use of ठीक is emphatic. It can emphasize proximity of distance or time, etc.