Is turbotax incorrectly calculating the long term capital gains on cryptocurrency? The 2021 rates should be 0% for the first $40,400. This does not appear to be the case.

You misunderstand how capital gains tax rates apply.  It's not 0% on the first $40,400.  Your personal capital gains tax rate is 0% if your filing status is single and your total taxable income is under $40,400.  YYour entire capital gain of $45,000 is taxable at the 15% rate since your taxable income exceeds $40,400.  TurboTax is calcuating your tax properly. 

If you cannot pay this tax when you file you should still file your return on time and pay as much as you can (or at the very least file an extension of time to file- which does not extend time to pay).

The IRS will let you pay in installments if necessary.   The penalties for filing late are greater than the penalties for paying late. 

Long term capital gains are taxed at 0% if your tax bracket is 12% or less (less than $40,525 of taxable income for Single filing status)..

However, long term capital gains are included in your taxable income for the calculation of your tax bracket, and that part of long term gain which crosses over $40,525 is taxed at 15%.

Please read this IRS document for more information.