The label on Scott's Premium Topsoil does not list any fertilizer or perlite. It does note that it may or may not be made up of a bunch of ingredients, some possibly unsuitable for leopard geckos (food waste?), but is different in different regions (which makes it very hard to recommend responsibly to someone who doesn't live nearby). It isn't actually 'topsoil' either, but that's neither here nor there I suppose.
Best to use the "topsoil" for its intended purpose and use something that's not a mystery product for the gecko. If what you're doing is trying to add moisture-holding capacity to the sand mix, peat would do that.
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