Upvote:2
According to Jeffrey Tigay, Professor of Hebrew and Semitic Languages and Literatures at the University of Pennsylvania, Book of the Covenant refers specifically to what was given in Exodus 20:19-23:33, which begins The Lord said to Moses: Thus shall you say to the Israelites ....1
The word translated in the ESV as "Law" in Deuteronomy 29:21 is "torah", which also means "teaching". The Jewish Publication Society Tanakh version of Deuteronomy translates this verse as:
The LORD will single them out from all the tribes of Israel for misfortune, in accordance with all the sanctions of the covenant recorded in this book of Teaching.
As such, it would refer to all the books that Moses was in the process of writing (i.e. the Pentateuch) and which today are referred to collectively as the "Torah" by Jews.
So in a sense I think you are right, although the Book of the Covenant is not really a separate book, but rather a subsection of the greater Torah (Book of Law/Teaching).
1 The Oxford Jewish Study Bible (1st ed.), p.162n