Awesome that fixed it thank you. Is there a way to Empty the pack into a chest like shift clicking the bag on the chest or something?
No, the 'Auto-Collect from Inventory or Chest' key can be used to load items from chests but there is no shortcut for emptying a backpack.
Pipes/hoppers can be used to pipe items from a placed backpack into a chest but that (usually) takes some time, you can however duplicate your placed backpack so you can have a copy with you while items are continuously piped out of the original.
Is there a way to reverse the resize because I lost a lot of my items!
The only item that gets removed when you resize a backpack is the backpack pouch, so unless a catastrophic error occurred you shouldn't have lost any other items.
If you've made your backpack smaller using a backpack resizer (or by using a backpack pouch on a world that had misconfigured backpack upgrade levels or had been configured to include backpack 'downgrade' levels) the items will still be stored inside the backpack but won't be accessible until the backpack is made bigger. You can make a backpack bigger by using the creative-mode backpack resizer item or by using a backpack pouch (provided your config includes another backpack upgrade level).
You could also try using a backpack restorer, but if that doesn't work something unexpected must've happened and your items will be lost.