Strategy for POP! Slots Casino?

Hi,

I'm trying to do the Swagbucks Pop! Slots Casino thing, but I can't seem to gain any more chips by auto-betting. I used the guide to get a lot of chips in the beginning but ended up losing them. Now I'm on level 25 with like 6 million chips and don't know how to get all the way to 33. Which strategy should I use to accumulate chips by auto-betting? I've been mostly using the fire lightning game until now.