Thanks so much for reaching out!
Unfortunately, stock does not automatically get reduced if a ticket is marked as Pending Payment. You can try to manually reduce the stock either on the WooCommerce Product Page, using the total_sales custom field or on the Order itself if you enable stock management.
You can also add this idea to our Feature Requests, as we tend to implement ideas based on customer feedback, so your input is greatly appreciated:
https://tribe.uservoice.com/forums/195723-feature-ideas
Let me know if this helps!
Thanks,
Jaime