Note Form 8453 states "Form 8949, Sales and Other Dispositions of Capital Assets (or a statement with the same information)" so you can just send the 1099-B as the "statement with the same information" you shouldn't need to fill out 8949.
This generally happens when you enter 1099-Bs as sales summaries but they have adjustments for wash sales, AMD or non covered categories. To avoid in future years, if you don't have many adjustments you can enter those "one by one" which will send Form 8949 electronically with the details, and input the rest of your 1099-B as sales summaries without adjustments.
