Advice for flying alone with a 4 month old?

It's a 7 hour total travel time. I can't afford to buy her her own seat so she'll be on my lap even though that's not the safest option it's all I can pay for.  And like I said I'll be alone. So I'm really nervous. I don't breastfeed so I can't nurse during take off/landing.... super anxious about having to manage her and everything else by myself. Also, we leave at 2 pm and don't arrive until midnight and there's a 3 hour time zone change. How can I attempt to somewhat keep her on her schedule of going to sleep at 8-10?? 😫 sAnd how can I keep her entertained, or get her to sleep, and also sleep myself? What if I need to use the bathroom while on the plane? I can't just hand her off to a stranger. She's not really into being worn but I guess I'll try anyway.  Please help lol  Oh and not to mention she gets her 4 month shots 3 days before we leave...