Upvote:2
Do they have an electronic record?
Yes, as mentioned in the comments, https://i94.cbp.dhs.gov shows the electronic I-94 record. If it's different than what's written, that means one of them was a mistake. Print a copy of the electronic I-94 and save it forever, as evidence that the written date on the entry stamp was a mistake. The site usually won't show this record after you leave the US, so print it now.
Will it [the wrong written date] be a problem?
Maybe or maybe not. If you're leaving before the electronic I-94 end date and not returning to the US for a while, it's probably fine. OTOH, if you apply for an H-1B or another immigration status that requires adjudication in the future, it could be an issue to have to explain why it's a mistake.
Should I contact someone?
It's up to you, but I would request a correction just to be extra careful. Most CBP ports of entryCBP's Deferred Inspection Sites will make I-94 corrections in case of mistakes CBP made on the entry stamp or electronic I-94. Many of the sites are at airports and are open Monday-Friday in the morning before most international flights start to arrive. Bring all documents but mainly the passport and printout of electronic I-94, and they should correct the entry stamp.