Science degree

Maths isn't required but it is useful - moreso than Economics, for both science degrees in those areas and for Economics degrees.

You will need to do a similar level of maths in your degree if you pursue Chemistry if it's not required, except much more quickly with much less individual attention. For bioscience courses you normally don't need as much, but it's helpful to have before as it'll make some of your modules easier. For other related STEM courses, like Earth Sciences and related areas, Maths is very helpful and not infrequently required.

It's also realistically required for Oxbridge STEM courses, if that was a consideration - the "no Maths route" in Cambridge NatSci doesn't really exist and it would be very surprising if they accepted someone without at least AS Maths, and it would again be surprising for Oxford to accept a candidate without three STEM courses for one of their relevant degrees, where Maths is the most relevant (with the exception of Human Sciences, which doesn't have any specific requirements, but indicates both a good mathematical background and a good scientific background is "useful", and possibly Earth Sciences or Biological Sciences at some colleges, if you did Geography/Physics - maybe).

Outside of Oxbridge though, the original advice applies in general. Realistically, mathematics is the language of science - even biosciences, albeit primarily statistics with a touch of calculus, as opposed to the fluency in the physical sciences - why would you not choose to pursue it if you are interested in science?

Should I do 4 AS though or just drop econ?

If your school allows you to drop one after a year (either taking the exams or not) that's reasonable. However I'd still suggest keeping Maths to full A-level either for the sciences or Economics, unless you really struggle with it and know you will study a less quantitative science.

I'm struggling with some topics and it's hard to find resources online as well because it's new spec this year. I guess I could try 4 AS to give me more time to decide then continue 3 to full A level probably econ I want to pursue science so I'll just have to keep practicing maths

You can use the old resources - the "pure" content is largely the same as C1-C4 from before, with I believe a couple odd topics from old FP modules included, and the "applied" content is to my knowledge basically M1 plus a little extra and a little less than the content of S1.

The fundamental mathematics however isn't different and while the style of the questions may have changed somewhat if you understand the maths then it doesn't matter, which should be your goal (of course in a pinch learning some question/exam style techniques is useful to maximise marks and/or scrape a few extra, but the core curricular knowledge is the main goal - and I believe part of the new format is to emphasise that anyway).

Additionally you don't need to use A-level specific resources - maths is maths, no matter what country it's taught in. Khan Academy and Paul's Online Maths Notes both have a number of useful videos/pages (the latter primarily for calculus, the former a bit more breadth and a bit less depth - you can actually follow along the latter to university level maths if you are so inclined). Mathsrevision.net was a site devoted to the old A-level syllabus - it hence moved into a more general A-level revision site but the content is largely the same, and I believe the redirect still exists (I'm not sure what the new url is). Whether this has changed for the linear syllabus I don't know, but see above again.

Also - ask your teacher. School and 6th form give you unparalleled access to your educators who are much more familiar with your specific work and where you fall short as well as being more able to provide individual support. This is something that is much more limited and harder to chase up at university, so take advantage of it as much as you can.