Large prints 16x20

Hi, I am new to photography! I print 8x10, 10x12 prints no issues. Looks like how I edit them. When I go to print a 16x20 the print comes and looks good only far away. Up close, looks blurry. I learned out how to resize a photo when larger wasn't recommended. I was excited to order that, then I got it and it's not right up close. Can someone tell me how to fix that issue if it can be fixed.?! Thank you for you times. Sad & frustrated.