I am a beginner in the game development world, I have just one quick problem with the UI, as you can see during the Unity Player, the UI (Raw Image w/ Texture) is normal in size but when I build my game to APK or EXE and run it, the UI is small. Why is this happening and how to fix it?
From the information you provide it is most likely to assume that the elements that are getting wildly resized are all UI-Elements.
When placing UI-Elements, by default, Unity puts them into pixel-fixed positions rather than relative-positions. To fix that set the
Ui Scale Mode on the
Canvas holding all your UI-Elements to
Scale With Screen Size, as detailed in this answer on Unity Answers.