Hi ptr159 - welcome to the forum!
All the Micro Scalextric systems - Scalextric Micro MR1 (1994-6), Micro Scalextric (1995-2019) and the new Micro Scalextric (summer 2019 onwards) - have only one radius size of standard curve. That means it is not possible to build a track with four lanes running side-by-side around the circuit. Other 1/64 scale systems that do offer this feature include Tomy AFX and Tyco/Mattel. Micro Scalextric cars will run on these track systems.
However, there are a few ways to build Micro Scalextric into a four lane layout.
1) The 1995-2019 track system does have a hairpin turn. This fits inside the standard curve with a significant gap, so doesn’t look great. It is also a 180-degree corner, so track design is pretty limited - but could be combined with the second option...
2) You can use the standard curves on both lanes - there will be gaps and you’ll need to use different length straights to line everything up, but you will get a four-lane track. Designing with a computer program (eg Ultimate Racer) will make things easier!
3) Build a ‘mirror’ or ‘butterfly’ track. This is where you run a long four lane straight (the body of the butterfly) with the rest of the circuit going off opposite directions - identical, but a mirror image (the wings of the butterfly). I’ve seen this layout used and it works nicely!
The new track system will be released next month (June 2019) with a My First Scalextric set. Currently there is only one corner radius, but Scalextric are keen to develop the system - so more corners are not out of the question at some point down the line. I certainly have my fingers crossed...