How do I limit quantitys on my products?

I only have 8 products per time slot, but I don't see how I can restrict my payment widget to show that. Can you help? I want to set it up so that once all 8 are purchased, it doesn't allow any further to be pruchased.

Unfortunately it is not possible to limit quantity of products, inside of payment field. 

Possible workaround is to use Ticket Purchases widget and Form Calculation widget. You can perform calculation inside of your form and pass calculation to payment field. Inside of this guides you can find out how to perform calculation in the form and how to pass calculation to payment field:

How to Perform Form Calculation Using a Widget

How to Pass a Calculation to a Payment Field

You can also use following widgets:

Inventory

Quantity Gift Registry

Gift Registry

Hope this will help. Let us know if you need further assistance.