I’m a new seller. Need PPC advice.

I’m a new seller on Amazon. I’ve been running PPC campaigns quite successfully for my product. I can see that I’m spending a lot of money on ‘Rest of Search’ and ‘Product’, but getting very little out of it. On the other hand, ‘Top of Search’ is working out great.

What I want to do is increase my placement bid for top of search (which I did) and make sure that my product doesn’t show up in the other two placements. However, there’s no negative bidding on Amazon and I can’t find a way to stop spending money on placements that won’t get me sales.

Any advice would be highly appreciated. Thank you so much!