Why do my mobile designs look bigger on screen when the devs program them? I hand over the designs through zeplin so they should be accurate

I am still new to UI/UX and I have noticed that the first 2 mobile design projects I have worked on and handed them over to a dev team through Zeplin, the designs end up being a bigger size on the screen then they are on my actual designs. Can anyone please help me with how to resolve this issue?

I am working on making them responsive but they even tried the correct measurements on the correct screen size and it still was larger than it should be.