cant stop natural yeast

All,
New to wine making, been brewing for a while. I picked 5 gallons of california petit syrah juice from my lhbs. It was cold when I got it, so I opened it up and noticed it was slightly carbonated. I added some tartaric acid to drop the ph to around 3.4 to 3.6 and added 1/4 tsp of potasium metasulbite to kill the natural yeast. Covered the buckets with a sanitized towel and went away for the day. I came back last night and it was fermenting like a race horse. I added another 1/4 tsp of metasulbite. This morning it was going even crazier. I pitched my dry yeast figured it can't hurt.

Did I do something wrong. Was I fighting a loosing battle with the natural yeast since they alreay reproduced? Should I worry or just sit back and enjoy the ride and hope the natural yeast are good ones.

Meta doesn't kill yeast. Your only hope is that the natural yeast is weaker than the dry yeast you pitched. If so, the natural yeast will act as a nutrient and the pitched strain will eat them off.

Enjoy the ride, you may like what the natural strain does anyway. You will never know until you try it.

Assuming the bubbling activity isn't from something other than yeast (an infection or MLF etc) If you throw any more yeast at it, you may want to consider a "killer" strain like K1-V1116.
But as WIP said, whatever yeast is currently acting on it might turn out well, too.
How does that saying go? ... "life is like a box of chocolates ..."

Well she is rocking, sounds like machine gun fire. My muscat that I pitch dry yeast finally took off also. Can wait to get home tomorrow night and take a look. My garage smells so good.

Thanks for the responses.