I sanded my last coat of epoxy and ready to apply clear coat. I did 180 grit on most of it but in spots that had a lot of resin to level out I used 80 griot then passed over with 180 after.

Now I did a final 600 grit wetsand in preparation for clear coat but as you can see in pic some areas seems to still show some 80 grit marks? I went over few times but it won't remove those. Is that fine? Can I proceed with clear coat?

No, you will see those scratches very easily. Worst bit is they may actually look acceptable as soon as you spray it, but over time the clear will sink back into those scratches and it will look worse and worse.

You need to progress through the grits, you can't skip from 180 to 600. I would start again from 120 grit in the areas you sanded with 80 grit, then do 180 all over again, then 240, then 320, then 400, then 600. You could potentially skip from 240 to 400 and just sand more with the 400, but I find it is less effort to go 320 then 400.