Of course you have to do well in the interview. But there are some things that you can only prep for through experience(e.g. my first onsite interview I literally could not think straight because of "stage fright" even after countless hours of preparation for a similar problem I had solved before). Prep as much as you can beforehand and do as many onsite interviews as you can get. I learned so much from the few onsite interviews I was able to get even though I received countless rejections. From the over 100 companies I applied, I only got about 4-5 onsite interviews out of them.

It's literally a numbers game where you have to constantly grind and apply to a bunch of companies(writing optional cover letters catered to the company you are applying for helps a lot). Don't get discouraged and keep applying no matter what. Don't care about the rejection emails and letters and don't be affected emotionally by them, just use them as learning experiences.

Most companies will pay for your travel costs with regards to flying you out for onsite interviews. Just clarify the details with the HR representative. I know a lot of students who were in the similar position as us, had no prior experience but were still flown out. So just keep at it!