It looks like you’re directly adding a brace, which is the “same level” as a bracket, whereas what you need is a sub-bracket. Sub-brackets appear as brackets by default, but you can switch them to appear as a brace (but at the same higher-level to the main bracket). This is now a layout option in 3.1, so is in Setup > Layout Options > Brackets and Braces > Secondary bracket appearance. This option would apply to all sub-brackets in the layout.
3 Likes