There are many reasons why your design could be showing with different sizes, so here are some suggestions:
If it is a prototype issue, you can set a proper fit or zoom level in the app and/or prototype viewer by using the zoom menu at the top right of the screen on your desktop app or browser or by tapping the screen with two fingers on your phone and selecting the appropriate scaling preset.
If you have designed the screens with the wrong size/proportion, you’ll have to resize the frames and make the adjustments manually. If you have set auto-layout and frame contraints for the elements on your screens then it will make the job easier.
If it was the case of you designing at the wrong resolution scale (say @3x instead of @1x) you could use the scale key (K on the keyboard) to scale the screens to a percentage of the original size (like 50% or whatever solves the issue for you).
wow thank you so much for your reply! I really appreciate you taking the time to help! thanks to you i’ve figured it out 🙂 I really appreciate it !