I'm setting up an item that if ordered, you get to select 2 out of 4 items to go with it for free. For example, they donate $100 and get to select possibly a mug, CD, shirt or picture for free. My current setup I chose was an item called "$100 Pledge" and it has attribute name of "choices" with values of "mug", "CD", "shirt" and "picture".
It shows up on the sales item page correctly, but if I check "mug" and "shirt" for example, when I add to cart, I get "out of stock stock available: 0" If I only select "mug" it works. So, if I check more than 1 box, it gives the out of stock error. What am I doing wrong?

Also, is there a way to limit them to only 2 checkboxes at a minimum and maximum? Or at least 1 and max 2?

Thanks in advance!!