WP nonce field checkbox prints checked=’checked’ outside input field

This is because you have used the checked() function, which echoes its value, inside another echo statement. If you are adding a value to a string you need the function to return a value. This can be done by setting the third argument, $echo, to false:

echo '<lable for="zoom_activity_state"> <input type="checkbox" name="zoom_activity_state" value="' . $zoom_activity_state . '" class="widefat" ' . checked($zoom_activity_state, true, false)  . '/> Is comming soon?</lable>';

You’ve also spelt <label> incorrectly:

echo '<label for="zoom_activity_state"> <input type="checkbox" name="zoom_activity_state" value="' . $zoom_activity_state . '" class="widefat" ' . checked($zoom_activity_state, true, false)  . '/> Is comming soon?</label>';