If entire 80% of an indirect transfer of pension is deposited to another retirement fund, what happens to the 20% withheld for taxes? Is tax then only on 20% not rolled?

That is, the 20% tax mandated is based on the entire $ available from the transferor & I do not have the “other resources” to make up the 20% difference to deposit to the transferee. So technically I should only be responsible for taxes on the 20% which already was taken out and considered income, yes? I wanted to do the direct transfer but missed the deadline (family matters, and poor correspondence from the transferor).