First job in about a year starts tomorrow. How can I remove some of the stress from my shoulders about it?

Brain is in meltdown mode and I know I’m being lowballed. My friend said to stay 3 months. Replenish savings and move to another place that actually pays. It’s a career change too. But I was burned by my last employer and I’m scared. I don’t know how to protect myself while still being friendly and pretend like there’s nothing wrong.