There are two files that are created of significance the Lightroom catalog file which is the database file with an extension of .LRCAT(.lrcat) and the Previews file with an extension of .PREVIEWS.LRDATA (.previews.lrdata). My info is as follows
Number of photos in my Catalog 27,497, the Catalog file is 408 MB and the Previews file is 28GB. The previews file can grow very large particularly if you create a lot of 1:1 previews.
What you are seeing is not unusual.