Is This Plagiarism?

[whatthehellamidoing]

Hello everyone, new user here!

Recently I submitted the final draft for my Math IA. However I have a concern: I actually based my topic about modelling graphs off another IA I had found online and took inspiration from it in the beginning parts of my IA. For example, the premise was set the same way since both of us got our data from the same reliable website that only provided data starting from a specific year, which meant our domains and axis for our graphs were the same. I thought the other IA had explained the foundation methodology pretty well so I basically followed the flow of their explanation with my own words, but of course the content reads alike, since there aren't many terms I can actually paraphrase as they're quite descriptive and technical. The parts in my IA that are similar to the other one are roughly about 300 words out of 3000? But the rest of my IA though is completely different. 

My teacher never contacted me about concerns of plagiarism after I submitted both my first and final draft (we hand our drafts in via turnitin but the similarity % is not shown to students), so I don't know if I'm overthinking or if I should legitimately be concerned that the IB will view this as an act of plagiarism, which was not my intention. I heard that the IB uses another program to check, so even if turnitin didn't notify my teacher of how similar those specific parts are, I'm still really anxious. I didn't cite the other IA as inspiration or reference, so I'm even more worried now. 

I'm actually scared out of my mind- of course I did not mean to copy, as proven by my completely different investigation, it's just that our "aim and approach" section and topic are really similar. Does anyone know if this constitutes as plagiarism from the IB's POV? And how serious it is? I don't know if I should ask my teacher about this because it'll just make it seem like I am guilty. 

Thanks and sorry for the long post!