At the time of passage the economy was measured in GNP not GDP and the USA did not rely on trade to keep its economy running. Trade was an after thought as the USA was virtually self sufficient in everything as the Nazis found out a little later on. The GNP is similar to GDP and the figure not adjusted for inflation is 90B. So how much of GDP did trade represent? The answer is that exports accounted for $4Billion dollars which was around 4% of the economy, a tiny amount of the economy.
So if Smoot Hawley reduced exports by 66% then the USA lost $3B or around 3% of GNP, tiny. A 3% loss in GNP is not even 1% per quarter. It is not good but had almost zero effect on worsening the economy.