"There are two parts on this spreadsheet" vs. "there are two parts in this spreadsheet"

The two statements do not imply the same.

There are two parts on this spreadsheet.

This refers to parts of what is on the spreadsheet, say a certain table of figures.

There are two parts in this spreadsheet.

This refers to parts of the spreadsheet itself, perhaps sets of columns, sets of rows, or such.

There are several ways of describing a spreadsheet that consists of two parts, but neither of the two you provide would the normal way be of doing so. What people might say include:

This spreadsheet has two parts.

This spreadsheet is divided into two.

There are two parts to this spreadsheet.

This spreadsheet consists of two parts.

I have divided this spreadsheet in two.

There are two parts to this spreadsheet.