If i was able to generate that seed it is possible that somebody in the future generates the same one
Thats why you should generate a very complicated seed...
This is a fundamental thing in whole crypto space. You have problems with any coin (also bitcoin), if you don't create a safe private key.
But if you generate a random one (for example with the algorithm of the wallet) you are fine. Just make sure, that you don't use the random function of powershell of the lately announcment.
If this still seems unsafe for you, because you are new to this whole private key thoughts, I recommend this:
https://www.weusecoins.com/amazing-math-bitcoin-private-keys/
I've already generated a 81 digits key
Can i make it stronger?
hopefully not, you need letters, as all digits besides 9 are ignored...
if you ment characters and generated with the wallet there is no need to make it stronger