OP is likely in a hospital as we speak...
If you do get caught with this stuff, there isn't much you can do. It is used for other purposes, but none of them pass as likely excuses. If you do get caught, they are going to want to send you to a hospital, unless you can talk them out of it. That would require a reliable support network of friends and family who you will argue will do a better job of taking care of you than a psych ward. Mental health workers aren't stupid; they know psych wards are pretty terrible places and in my experience, would rather try alternatives, if they exist. If they do, you must stress a willingness to aim for recovery. You will basically have to volunteer yourself to be watched pretty rigorously by family and friends. You probably won't want to do these things, but if you want to stay out of hospital, you have to give the doctors some reason to believe you will be alright without being admitted to a ward.
Someone also mentioned trying to hold on to the SN; I don't see that really happening. If people find it and it's a big enough deal to get doctors involved, they are gonna want to take it off you and I'm pretty sure they can. While it's not illegal to own SN, it's not about legality of the object, it's about duty of care between doctor and patient. If a doctor thinks you are a risk to yourself, they not only have a responsibility, but an obligation to deprive you of means to harm yourself. This will be by putting you in a hospital and making an order that your SN is disposed of, or by you voluntarily relinquishing your SN. It's really your choice. There is no situation where you both get to keep your SN and get to stay outside of a hospital.
I'm not a mental health worker or anything, but I have successfully talked my way out of being hospitalised on a couple of occasions. And also been hospitalised on a couple of other occasions where I handled the situation poorly. Cooperation with the health workers is the only way you get to go. Be difficult and you give them more reason to hospitalise you.