The Medrash Rabba says that Moshe Rabeinu was perplexed how the yidden could build a mishkan. Hashem told him that every Jew can build it on his own because along with the mon there came down precious stones so they were all wealthy.
The Ksav Sofer why Moshe had difficulty understanding that they cold build it? Surely he was aware of the wealth they had received due to the precious stones which came down with the mon. He answers that Moshe’s question was that he couldn’t understand how a mishkan made mostly of gold could be a kappara for the egel hazahav, the golden calf. As per the rule of ein kategor na’aseh saneigor, we never use something involved in the aveirah for the purpose of getting a kapara. This is the reason that the kohen gadol doesn’t wear gold clothing on yom kippur.
Hashem answered Moshe that the kappara was not being accomplished thru their donation of gold to the mishkan. No individual’s money was truly needed because every yid was so wealthy that he could have built it alone. Instead the kappara was that by building a mishkan they were showing that they beleive that they can bring the shechina directly into their midst without any 3rd party between us and Hashem. This was a kappara for the egel where they thought they need an egel to be a link between them and Hashem. The act of donating gold and silver was only a means to show that each individual wants to be a part of bringing the shechina to their midst, not because that individual’s gold and silver was needed. Therefore the original question falls away. The gold was not the kappara – the desire of every Jew to bring down the shechina was.