I've been on T for more than six months now but I just had an accident where I don't think I actually injected myself. I pulled the needle away and wiped the back of my hand over the spot I thought I injected and clear sticky fluid came away with it, which I think was the T. If I didn't actually inject myself, should I try again?

On a related note, if I open a vial of T but don't need it, can I put it into a plastic bag/leave it out until I need it?

If you emptied your syringe and didn't get a bleeder there's a good chance you're fine. A little leakage is a common side effect of non z-tracked injections. And yes you can store a vial with top popped wherever as long as it's stored in room temp away from sunlight.