That is two amplifiers. Try a gain of 30 as a start. You will probably need to go lower.
Apart from that make yourself a Spider antenna for comparison to check if your colinear is any good.
Where is your antenna mounted?
This is also always interesting to know:
(What is the Maximum Range I can Get?)
As a very rough guide to set gain:
Displaying the RSSI in SkyView:
Click on expand sidebar:
Click the column head of RSSI twice so the numbers closer to zero are first:
If there are many entries larger than -3, for example -2 you can reduce the gain.
If that RSSI of -2 or -2.5 happens very rarely you are just fine in regards to the gain.
If all entries are smaller than -4 then you may want to increase the gain.
If you have aircraft that vanish as they fly close by at low altitude that normally means the gain is too high to receive those. But if you don’t care about that you can optimize for plane further away. But that does not necessarily help to increase reception far away.