photos are really dark when exporting to jpg

Dear Friends

I am wanting to export my edited images for print. I have exported them to JPG to save to USB. When I select the image i want to export it darkens the image by quite a lot in the preview. If I select Original + Settings it looks fine but the printer at the store does not recognise CR2 files. How can I export to Jpeg and retain the image colours etc.

Using latest macbook and LR.