I will always recommend bought masks as they are done properly to scale.
Kudos to your first attempt, but the red circle is a little large. Never mind this is very much a learning process.
Now for the colours for RAF insignia.
White - Use Vallejo insignia white.
Yellow MRP RAF WWII Marking Yellow. for roundels and ID strips. This is a match to the chipset. RAF training yellow for training aircraft is a different shade.
https://mrpaint.sk/farby/lietadla/RAF?product_id=184
Marking Red. Used on roundels, stencil lines, text and squadron codes/serial numbers on night aircraft etc. Match to Chipset
https://mrpaint.sk/farby/lietadla/RAF?product_id=185
They have 2 blue colours. The one you should use is BS 105 Oxford Blue
https://mrpaint.sk/farby/lietadla/RAF?product_id=185
Spray them to full colour depth.
Day aircraft squadron codes use Vallejo RAF Sky 71.302. This is a chipset match to BS 210.
Always be prepared to look at using different paint brands to get what you need. AK and Mig Ammo are not as pigment rich as Vallejo and they have a policy for "Scale correct" paints so the same colours will be not a chipset match but lighter. I will dip into their colours if I have to, but am not very keen on them.
I use MRP, Vallejo Model Air, Vallejo Metal Color, AK Xtreme Metal and Tamiya X-13 which is an acceptable version of Japanese Aotake, but I never spray that one, I always use a paintbrush.
The more insignia you paint then the better your masking techniques will get. If you can, use Kabuki tape masks, and be prepared to make alterations for spacing, getting round lumps, bumps etc. It does take longer, and you need to think about how you are going to do it.
Also, make sure the base camo coat(s) are 110% cured and dry!
James