There are two ways that you can go about this, XTC.

Firstly, you could go to your Mom and apologise to her for 'letting her down'. This will achieve two things. 1) it will show her that you care about how she feels, and 2) may open communication between you both, so that you can assure her of your 'responsibility' in taking the drug, and that you are well aware of the facts pertaining to such (be armed with sound knowledge of the 'pros and cons').
Ok, she might not relent or be happy about you doing it, but at least you can 'clear the air' (sorry, no pun intended) and be on good terms with her.
After all, the thing that she is thinking now is, "have I driven my son into some kind of rebelious mood?", and "what other drugs is my son doing that I don't know about?", etc etc.

Or, the second option is to move out.
But, seeing as moving out will be seen by her as a rebelious thing to do, she will start thinking of all kinds of wierd stuff that you might be up to, and it will make her worry even more.

I suggest the first option.
You have nothing to lose, but you might just gain yourself some valuable respect for your honesty. Put yourself in her shoes, dude, and imagine if you had found such a thing in your son/daughter's room...

Just my opinion, man...I hope it works out for you