Timeframe of the prediction
Chamath made the prediction around March 18–19, 2020, saying that in a worst case the U.S. would have mass testing within 30–60 days. That window runs roughly from April 18 to May 18, 2020.

What U.S. testing actually looked like in that window

• In the week of March 25–April 1, the U.S. was performing about 110,000 tests per day, but hospitals and clinics were still denying tests to people with milder symptoms and often had week‑long result delays, indicating testing was far from broadly accessible. (en.wikipedia.org)
• During the weeks of April 6 and 13, the U.S. conducted about 150,000 tests per day, while experts recommended at least 500,000 tests per day before easing social distancing. A New York Times report on April 26 concluded the U.S. still had not reached an adequate level of testing capacity due to persistent shortages of reagents, swabs, PPE, staff, and lab equipment. (en.wikipedia.org)
• A Harvard‑linked analysis cited in April 2020 noted the U.S. was averaging about 146,000 tests per day and estimated the country needed roughly 500,000–700,000 tests per day by mid‑May just to reopen safely, showing that even by the end of the 60‑day window the U.S. remained well below what experts considered "mass" or sufficient testing. (planetizen.com)
• By early May 2020, U.S. testing had risen to around 240,000–260,000 tests per day, but this level was still described in contemporaneous analyses as inadequate to contain the outbreak. (en.wikipedia.org)
• Per‑capita comparisons reinforce this: as of April 28, FactCheck.org, summarizing Our World in Data and other sources, reported that numerous countries had done more tests per capita than the U.S., underscoring that American testing remained relatively limited despite large absolute numbers. (factcheck.org) And as of May 16, the U.S. had performed about 32.4 tests per 1,000 people, still behind many peers and criticized for having been slow and insufficient in ramping up “crucial testing to contain the spread.” (statista.com)

Interpretation relative to the prediction
Chamath’s claim wasn’t just that the U.S. would increase testing, but that it would reach “mass testing” capability within 30–60 days. By mid‑April to mid‑May 2020, the U.S. had indeed ramped up from almost no testing to hundreds of thousands of tests per day, but:

• Testing was still heavily rationed, with many symptomatic people unable to get tested promptly, and long delays in results. (en.wikipedia.org)
• Major analyses at the time consistently described U.S. testing as inadequate to monitor and contain outbreaks, and far below expert benchmarks for what would count as broad, population‑level testing. (en.wikipedia.org)

Given that contemporaneous public‑health and data sources viewed U.S. testing during April–mid‑May 2020 as insufficient and not yet at the level needed for widespread screening and control, the prediction that the U.S. would achieve mass testing capability within 30–60 days from March 18–19 did not come true.

So the prediction is best scored as: wrong.