Yes, it's a goner. Do some reading on the cacti succulent forum, there's more than enough there for you to read without having to be regurgitated yet again.
You did at least three things wrong....read and you'll find out.

Also, it's not a lithops. It is a Pleiospilos nellii. You'll need the right name to find the proper care. :)

Nancy

Sorry for your loss. I will point out a few things but yes do some research online you'll find a lot of info.

Soil: Sorry to say, but almost nothing is right about that soil. It looks like it's 99% peat with some huge chunks of bark and twigs, which are all detrimental for succulents as they retain too much moisture. There's also some time-released fertilizer that you do NOT want/need for this particular succulent. Succulents in general need very fast draining medium and needs to be able to dry out fast, for mesembs (your plant included) you should especially consider a grittier mix, or THE gritty mix, if you could get the proper ingredients.

Watering: You should let it rest a few days to a week before attempting any watering. They need to settle in their new soil and environment first and their roots need to heal. You can tell if it is ready for some water if you lightly poke the plant and if it is a bit soft and not turgid then you can give it a drink. Also Pleiospilos nelii should only have 2 pairs of leaves maximum, and if the old pair of leaves are still being absorbed (you said smaller leaves shriveling up, that might be it), then you basically don't have to water it at all.

Sun: Is it getting enough sun? Doesn't have to be direct sun all the time but it's got to be pretty bright for this particular plant

And in general, these guys don't like to be repotted too often, so if you do try again make sure you really get the soil right the first time.

Good luck, these guys are really something interesting. I'm new to them too, but so far it's doing quite well

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