Routing 5 differential pairs over a short distance with limited space
First, with 800 MHz bit periods, you can afford at least 10 mm, probably 20 mm length differences between pairs. From the perspective of getting the signal decoded correctly, you could also allow ~10 mm differences within pairs, however even small intra-pair length differences cause common mode currents, which lead to radiated signals, so it's better to keep the two lines within each pair well-matched.

Second, it's preferable to route your pairs as actual pairs, not just as separate lines with the same length. For example, you could do something like this (sorry, I used red for the layer you have in blue and blue for the layer you have in salmon)



The main point is that for as much of the trace length as possible, the two lines of the pair are actually routed directly next each other. Symmetry in the break-out from the chip or connector pads ensures (with a tiny bit of tweaking) length matching.