The quantity of my products was calculated improperly.
Cart2Cart provides an opportunity to calculate an approximate time and cost of migration. You can make this procedure via Migration Estimator. Specify your Source and Target shopping carts. After that fill in the quantity of products, customers and orders you would like to migrate.
Note: Cart2Cart calculates only the quantity of parent products, so, in case your store includes child products (variants), they may not be counted. However, all of them will be migrated.