wakeop

This .quiz-form label code is intended to create a block view of inline elements. Because the font size in your theme is in pixels (at 14px base in body), there may be a conflict between the theme’s css and the plugin’s css. Then the checkbox / radio button distance may be greater than 2.25em.
Try to increase this value or put the appropriate value in pixels.

For example, in Additional CSS you could put the following code:

.quiz-form label {
???? max-width: calc (100% - 31px)! important;
}

Start from this value and increase until it stops moving.

Try to put the following css in Appearance -> Customize -> Additional CSS:

.user-answer>span {
    font-weight: normal !important;
}

If the theme css is loaded before the css of the plugin, you can add the following code in Additional CSS:

.quiz-form label {
    display: inline-block !important;
    max-width: calc(100% - 2.25em);
    vertical-align: text-top;
}

.quiz-form input[type='radio'], .quiz-form input[type='checkbox'] {
    display: inline-block !important;
    margin-left: 0.25em;
    margin-right: 0.667em;
    vertical-align: -0.15em;
}

If the css of the plugin loads before the css of the theme, nothing can be done for the time being. This visual problem was solved in the Watu PRO version, but not in Watu Quizzes yet.

The font size is set by your theme and you can change it for the whole theme as well as for Chained Quiz.
If you want the change to be for Chained Quiz only go to the Appearance -> Customize -> Additional CSS and try with this code:

.chained-quiz-choices {
	width: 50%;
	margin: 10px auto;
	text-align: center;
}
.chained-quiz-choice {
	text-align: left;
}
.chained-quiz-label {
	font-size: 16px;
}

You can change the value of font-size until you get the look you need.