I got a job offer to cover a maternity leave, but I found out I m pregnant too

I got a job over to cover a maternity leave, but I discovered I am too . I didn’t expect that they would make me the offer, but they did and it’s my dream job. I ve always wanted to work for that specific company. So I ve been offered the contract but then before signing I decided to tell them. They told me they cannot take the offer back, which surprised me ( I had literally no clue) and initially it was a positive feedback. However then they told me that it would be very unfortunate for them, and they kinda suggested to refuse the offer because they cannot take it back. I love the job and the opportunity. What shall I do ?