UK STEP

Hi there, since I am applying for maths at university I have an option to do STEP (Sixth term examination paper), and if I do well then I would be offered academic scholarships, lower entrance grades etc.

I was wondering if universities have direct access to STEP because if so, I might not do it in the fear I would do bad and they would instantly be able to see it.

I am quite decent at maths, I'm predicted an A in further mathematics but STEP is extremely hard, if universities didn't have immediate access to it then I'd have no reason to not at least attempt it.

The bit in bold seems to be phrased in a rather strange way. Having an option to do STEP isn't an automatic consequence (or requirement) of applying for maths at university, and indeed isn't at all necessary for most unis. Are you saying you have applied specifically for a (UK) university that includes STEP as an alternative part of its standard offer and says in its course prospectus that you can get scholarship benefits for having it, or are you making an assumption about the importance of STEP?

Some things to consider:
STEP I (the 'simplest' variant, requiring only non-FM content) has now been scrapped, so you would need to be confident at FM and looking at STEP II and STEP III papers.
Last summer, STEP could only be sat by those people for whom it formed part of their offer. This was all due to Covid so should not apply in 2021, but don't pin your hopes on it.
STEP requires a lot of preparation to do well. It is not unknown for people to drop grades in their A levels because they've devoted a disproportionate amount of time to STEP and neglected their A level work. Remember that A levels are relevant everywhere, STEP is very niche! You don't want to ruin your chances of getting into any of your 5 choices just by focusing on one element of the application.

Personally I would be trying to get my FM prediction up to an A*, but it's your choice at the end of the day.