You can easily remove estimates that have already been importing from the queue. This would only happen in a very odd circumstance, like Internet going down.
1. Go to the Quickbooks menu in the grey dropdown menu in LMN, then choose Quickbooks Export.
2. When that screen loads, click the EXPORT QUEUE tab. That will show the estimates 'stuck' in the queue. Just hit the DON'T EXPORT button to remove them from the queue.