It's a different site altogether. No critic or employer cares about this kind of stuff to the extent they'll discredit you. Now, if you'd selected the exact same site and copied every detail of the Snohetta project down to the panelization with no modification whatsoever - then yeah, you'd be questioned but not as much for "plagarism" but you failing to demonstrate critical design skills in order to adapt a general building type to your specific brief.

Walkable landform buildings with a portion sticking out of the mound have been popular for a long time - even RPBW finished a massive one in Greece recently.

I'd be more concerned about the lack of drawing documentaton illustrating your design process and plans/sections than the idea. Ideas are everywhere. It's the execution that counts.

At this point, with as many buildings that have been designed (built & unbuilt), it is absolutely impossible to design a building that doesn't have some resemblance to another. The more creative works created in any way or form, the more likely you will have works that resemble another to some degree. Same with writing and even the same with music. Steal like an artist. That is, you can take elements from existing to create a new design. Building elements are like words and sentences or notes & sequences of notes. It is the whole composition that matters.

Relax a little bit. Don't outright try to take someone else's work and claim it as yours. Be inspired. Draw from multiple inspirations to design your own work that may draw from multiple sources of existing work to address a specific design problem at particular site locations & site uniqueness, and make a unique composition even if the individual elements are not entirely unique. 

In real world practices, your buildings are mostly going to compose of "off-the-shelf" components that are pre-manufactured and maybe customized on site.

I think it’s different enough, but I’d get rid of the grass roof, and instead make the benches that flank the edges into raised planters with small trees.  They can be different shapes or whatever.   Something like that will reduce the similarity of the first glance.  

you're completely fine... 

This is not plagiarism at all. you're fine.

This is hardly even similar. The absolute worst that could happen is someone would see it and be vaguely annoyed that it's similar and not think you're very original.... but I've seen some school projects that were formally very intense copies of fairly iconic buildings, like the Ministry of Transportation in Tbilisi, that people thought were nice projects. 

As a side note, you have to try really hard to do something I would call "plagiarism" in architecture. Enough building's have been built that almost nothing is original. While at the same time, if you build something vaguely like another building someone is going to call it a copycat, because that's just how people are. Had a recent personal example of this on a publication about a project I was involved in, where I am still scratching my head how someone would equate the two buildings. Interestingly there was another building I am aware of that looks much more similar to my project and I could see someone's critique, though it was really just a fairly simple design logic that two people in two different firms happened upon... happens.