Been there. I used to take professionalism too seriously. Gave it my 100%. But that got me nothing except headaches.
If your client is asking you to do this, inform your company manager about it. Make sure he/she is aligned with this. If they don’t want you to work on a weekend, let them talk to client. If it’s your manager who is asking this, make sure it’s on email. Just send a mail on the day you worked saying, you worked on this day and you need a comp-off for the same. Have these discussions before you work on the weekend/holiday.
You can’t say No to the work because you’re a fresher and you’re worried about job safety. If the work is bothering you a lot, talk to your manager, no matter how horrible they are, they will listen to you. If you’re still afraid, talk to an HR about company policy on shifting projects. Or find another project yourself.
It’s a lot better to shift project rather than suffering.