You could have taken six weeks off. You were legally permitted by law to take up to 12 unpaid weeks and still have your job waiting for you when you got back (assuming your employer had 50 or more employees and you had been working there for a year IANAL). Most people don't know that you can actually take up to 24 weeks, but if you do take more than 12 then your employer is not obligated to give you your exact job back, only a comparable one. You also didn't have to take it immediately after your child was born, but that you had up to one year to take your baby leave.

I wasn't paid for all 6 weeks. My wife and I had to save up a cash cushion (and her leave was paid because her company had wayyy better benefits than mine). It was a decision and an expense that was important for us, so we saved up for it because we knew that my wife would probably be out of commission for the first six weeks our boys were born and the first 4-6 months of twins is a crapton of work.

I never felt guilty when I came back to work. Once you really internalize that people in a company are replaceable, you just start preparing people for when you leave on vacation or baby leave instead of worrying about it.