You're doing it a bit backward, name the file to be created, then the files to be added to archive.
[user@home]$ file file.tar.gz
file.tar.gz: gzip compressed data, from Unix, original size modulo 2^32 1464320
[user@home]$ 7z l file.tar.gz
7-Zip [64] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21
p7zip Version 16.02 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,64 bits,8 CPUs Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (906E9),ASM,AES-NI)
Scanning the drive for archives:
1 file, 1358768 bytes (1327 KiB)
Listing archive: file.tar.gz
--
Path = file.tar.gz
Type = gzip
Headers Size = 10
Date Time Attr Size Compressed Name
------------------- ----- ------------ ------------ ------------------------
..... 1464320 1358768 file.tar
------------------- ----- ------------ ------------ ------------------------
1464320 1358768 1 files