Website doesnt look good on macbook air 13 inch

the margins are really bad on macbook air 13 inch
This is how it shows on 13 inch macbook.

This is the actual design

This is part of your design. You’re designing for each device, but for each device, there is not just one width, but a range of width. You have to make sure your design behaves well for the whole range. You can shrink and enlarge your viewport right in the deisgner by grabbing its edge and dragging it left and right.

Works for every device.

The MBP 13" probably shows the narrowest width, which you haven’t (yet) accounted for.

can I add breakpoints? I guess Macbook Air is something in 1366. how do I add breakpoint for it?

No you can’t, if mbAir registers on the tablet breakpoint then you have to make it work with it.

You can add breakpoints with custom code though.

the thing is. It looked good on large screen and my MBP 15. but i sent it to my friend that has MBAir 13 inch and she said it doesnt look that good. so if I add the tablet version. will it fix?