This is one of the challenges of 3+2 programs and the reason one of my kiddos chose not to pursue one. Students are eligible for 12 semesters of Pell, but if you completed the graduation requirements for biology at your first college you may no longer be eligible for the Pell Grant. You may not count the engineering degree as a second degree, but the federal government might. They don’t pay for 2nd degrees.
How many courses do you need to graduate? If your parents can’t pay then one option is to attend part-time as you can afford it, take an additional federal student loan (if you’re still eligible for any), and work for the rest. Another would be to take a gap year to work for the money.
You may also want to check the rules for graduation. I used to work at a college that participated in a dual degree program. If a student completed the requirements for one degree but not the 2nd they were awarded the degree for the major they completed. But I don’t think a biology degree will help you get a job that will pay off a $52k loan. Your best option may be to finish the engineering degree.
Unfortunately, I don’t think there are grants available to pay for a second degree which is what a 3+2 program ultimately is. You can check with the financial aid office to see if they have any suggestions, but try to figure out a workable backup plan just in case.
The good news is that you have a university within commuting distance of your home. Many of us have had to work our way through school. It’s disappointing and can be hard work, but it’s a viable path to a degree.