@Pushkinia I'm so sorry for your loss.
I lost my dad at a similar time. Yes, grief is definitely not linear and can hit us to different degrees at different times. I come from an Irish family, and today has been hard, as I remember St Patrick's Days in the past with my beloved dad.
It's lovely you're honouring your mum's wishes, and I know what you mean about it seeming final, but in actual fact I think there'll be loads more moments when you feel you're saying goodbye or communicating in other ways with the memory of your mum.
It was different for us, as the funerals culturally happen very quickly in Ireland, and burial is far more common. So, my dad was buried a few days after he passed away, and we were all still in such shock. I almost didn't have time to think of it as the main goodbye. I've found myself chatting to my dad many times since. I did today. I'm very spiritual, and believe in the afterlife very strongly; but even if you don't, you might find yourself chatting to your mum's memory, if that makes sense. I couldn't bear to think of the funeral as the big goodbye. I was on autopilot and can barely remember it to be honest.
I think you could maybe frame laying your mum's ashes to rest as an act of love, and love never ends, and is always ongoing.
I'm so sorry you didn't get an immediate response to your initial post. I dip in and out of this board, and I think many people do. So, I didn't see your message till a few moments ago, and probably the same for lots of us on here. But, it's a very supportive place, and I hope you can find it helpful.
You take care, and I hope laying your mum's ashes to rest in accordance with her wishes, can give you some peace and be a time of reflection. Thinking of you x