If I've donated cash and stock, is it possible to hit the 60% deduction limit? Based on my 2018 worksheet, it seems that I can only deduct 60% if it was all cash.

It depends. Yes, you are correct, there are different categories of contributions with different limits. Based on what you are donating and to whom you are donating, the percentage of Adjusted Gross Income deduction limit could vary.

In general, cash donations are limited based on 60% of Adjusted Gross Income. Capital gain property is subject to different limits depending on other donations that year (see page 16 of the link below). Any amount exceeding the limits would be carried over.

From IRS Publication 526: Charitable Contributions; Limits page 15, Carryovers, page 19

You can carry over any contributions you can't deduct in the current year because they exceed the limits based on your adjusted gross income. Except for qualified conservation contributions, you may be able to deduct the excess in each of the next 5 years until it is used up, but not beyond that time.

A carryover of a qualified conservation contribution can be carried forward for 15 years

Contributions you carry over are subject to the same percentage limits in the year to which they are carried.
For example, contributions subject to the 20% limit in the year in which they are made are 20% limit contributions in the year to which they are carried. But see Carryover of capital gain property, later.

For each category of contributions, you deduct carryover contributions only after deducting all allowable contributions in that category for the current year. If you have carryovers from 2 or more prior years, use the carryover from the earlier year first.

Carryover of capital gain property. If you carry over contributions of capital gain property subject to the special 30% limit and you choose in the next year to use the 50% limit and take appreciation into account, you must refigure the carryover. Reduce the fair market value of the property by the appreciation and reduce that result by the amount actually deducted in the previous year.