DIY sink - can someone help with my sink replacement?

[CarInsurance]

I've finally got around to replacing one of 2 sinks that had a chip on the bowl. I have opted for a slightly smaller sink than the previous (marble top was originally cut for slightly bigger sink but meant no room around the edge). I've watched a few YT on changing and bought plumbers mate etc. If it matters the plug has no overflow. This is the first time changing a sink so please be kind! I have another of the same to do as is a 2 bowl unit.

Issue: I've put the bowl in and think the pipe is pushing the plug upwards/the stem of the plug is too long for the bowl to sit effectively on the marble. This also mean the plug cannot be screwed up enough and leaks but also isn't draining fully and there is puddling around the plug within the sink.

I assume I need to remove the plug and cut the metal a few cm to allow the sink to drop? Or am I missing something else?

I usually fit the sink, and then plumb the waste pipe to it, so my approach would be to change the waste pipes. That said, as long as you are careful of burrs, I can't see any reason not to shorten the threaded outlet of the sink plug fitting. Take off a little at a time if you choose this route. You can always take more off, but you can't put it back on.

Thank you @HappiestSleeping. I have no idea how to change the pipes, so I think perhaps using a dremel to take a few cm off at a time might be the best idea!