When I send in a ballot via mail, I always call the voter office to see if the ballot arrived. Then, I just have to take their word that it did. This time, as in 2016, I expected to vote in person but wonder about the long lines.
You should put some kind of mark/word on the outside of the envelope and ask the clerk to read/tell it back to you - that way you'll know for sure if they got it and they're not just saying they got it.