If you mean you're doing alternate stroking but starting with an upstroke instead of a downstroke... it is kinda backward. Usually the first note of a bar is a downstroke so if you're trying to learn a song you'll be doing it backwards from the way it was written. Downstrokes and upstrokes also have a sound of their own (when you've been playing a few years you can hear whether it's a downstroke or upstroke by ear).

I guess in the big picture of things, you could get by doing it that way.... but if you can learn the proper way and start with a downstroke, you'll find learning to be a lot easier in the long run. (you're already making it more difficult by playing left handed so this just adds to the difficulty :)

I feel your pain tho. I know most drummers start playing rolls with their right hands but I have to start with my left. And piano's are backwards to me so I get how ya feel.