From Longman Dictionary of Contemporary Englishbe/get in over your headbe/get in over your headto be or get involved in something that is too difficult for you to deal with In business, start small and don’t get in over your head. → head
Examples from the Corpus
be/get in over your head• How loan scams operate How homeowners get in over their heads with home equity loans: 1.• We had a feeling they might get in over their heads and they did. 