WP E-Commerce Price Variation for Limited Stock Products

Hi,
I run a instruction business (teach self-defense and firearm training). I have limited seating per class (such as 2 seats per class). I want to give my clients an option to pay either a 50% deposit or the full amount when purchasing a class seat.

I notice when I make a price variation, I end up with 4 in stock versus just 2 (due to the 2 in stock for each price variation).

I just want to be able to sell the 2 seats in stock and that’s it, not 4. I have an issue of overbooking because of this. Is there a way to just have the two products in stock with a price variation? Thanks for any info!