If you stop using now, you have a chance. Meth will stay in your system for around ten days, but that will depend on how much you take, how pure it is, your age, weight, metabolism, etc.
As for your leg, are they likely to check you for needle puncture marks? I'm wondering if it is worth bandaging it and saying you were bitten by a dog or something if they ask what you have done.
Whatever you do, stay clean between now and the drug test. If you can do that, can you stay drug free for longer? I don't know if getting clean is something you have considered, but you would certainly save money and feel healthier.
If you are going to continue after your drugs test, stick to just smoking it. Needles can lead to all sorts of complications, and it's just not worth it in the end.
I hope the test goes well, stay clean until at least then, and you should be fine.
