I'm a bit unnerved by the "I think it matches" . The purpose of this sort of test is so we can know it matches! Thankfully we can test that if you have the regular GNU/Linux PC to test with.
If you take the SD card out of the DB410C and connect it to your PC then you should some of the partitions on the card automount. One of the partitions is called "writeable" and should contain your SSH public key and you can compare it byte-for-byte with /home/megha/.ssh/id_rsa.pub .
For me the key is found in (note that there might be an extra /var at the front for you):
You should check that the <user-name> you are using matches the directory name ("daniel-thompson-s" for me) and that the contents of id_rsa.pub and .../authorized_keys match.