Hi.
I also use my pinkie for power chords, although I often use pinkie and ring finger too. I'm guessing this is ok as I've seen instructors on this website as well as many musicians on the internet do the same. I'm going to link to one of the lessons by Mike where he uses this technique for B5 but then uses pinkie and ring for F#5. If it's good enough for Mike, it's good enough for me. However, as Billy says above, you really should learn pinkie/ring as it'll no undoubtedly be required in future.