Poor display quality from Illustrator to PDf

Hello,

I drew a plan on illustrator and when saving it as a PDF for my presentation, its display quality changes quality. The line weight isn't as flattering as it originally shows on illustraor, it appears much thicker in PDF which I don't want. This problem doesn't occur with some of my previous drawings. Would anyone be able to help me with please? I have an important midterm presentation in a week and I must fix. Thank you very much!

Best,