Hey and welcome, Brigid!
Sounds like you've already got a head start to most people here- heh! To counter your premature awakenings, try to practice this exercise in waking life whenever you remember it. Stop what you're doing and simply question reality, look at the details of things, observe how people react, etc. Then consider the thought "If i'm dreaming then.." and follow that up with what you'd like to do in the lucid dreams.

Good luck with your lucid dreaming journey and don't hesitate to send me a personal message or post on the boards