How can I export all the responses in one single excel file?

Hello mtirigall.

You can export all your form submissions to Excel file, right from your Submissions page: How-to-Export-Form-Data-to-Excel

We also support making partial exports of your form submissions: How-to-Partially-Download-Form-Submissions-as-Excel-CSV-PDF

Please let us know if you need further clarification or help with this, we will be happy to help.