Image uploader inside custom post widget

I’v built a custom widget that will show some sport scores. Scores are added trough custom post. When i open new custom post(scores) i enter their team names, score, scores. Now i want to add an option to show team logos next to the team name. In the last couple of days every tutorial here and elsewhere i could find didnt worked. I have no idea why, as i am newbie with all this. With many of it, upload button appears but the pop up to chose/upload image doesnt appear. Now I could post at least 10 links where i found this codes but i believe there is a limit with link. So for an example this is most common tutorial i have found.

[Large code excerpt removed by moderator per forum rules. Please use the pastebin for all large code excerpts. It works better anyway.]

what exactly is this ‘my_plugin_page’ i guess i am doing something wrong and that’s why uploader doesnt pop up. What i need to add instead of it, any example?

Inside my theme i’v made a new folder called my-plugin inside which i added my-admin.js with the script code from the link above. Is this the right way?

I also tried other way without it and calling the script by get_template_directory_uri().

Any help pls.