Hello.
This is specific to the UK and GCHQ, but could apply to the USA and the NSA. Please take what I say with a gram of salt, as it is not accurate, it is just my interpretation as a PhD CS Student.
You are a small fish, even if you've googled Sodium Nitrate sources, unless you're also meeting other individuals in real life, a follower of certain violent beliefes or active in the distribution of child pornography, I doubt you are going to be checked. People have bouts of weird googling, there is case over here in the UK of a man being snagged on CP charges for having loli hental? How was he found? He told all of his friends about his server and one reported him.
Good chances, that if he kept quiet, he would have never been found out.
If you're not telling others you plan to CTB, I doubt you will be registered, every western nation is too focused on preventing extremist attacks to be bothered about one or two suicidal people.
Obviously don't be to brasen about this, but I think you can relax, so long as you keep your wants here, I think you will be perfectly fine. I hope this helps you relax a little.