Hey Oscar. I’m sorry to hear that! Hopefully we can find a way to recover your seed.
By design, it is virtually impossible to guess an entire seed. However, if you know most of your seed, that makes the process of recovering the rest of it significantly easier.
The process is the same either way – try random guesses until you find the correct one – and you’re still going to need to try a lot of guesses, but trying to find the last 13 characters is significantly easier than having to guess all 81.
Have a look at these threads to learn more about how people who had typos or other problems with their seeds were able to recover them:
The short version is, you’ll need to write a script (or find someone you trust who can) that fills in the missing 13 trytes, generates some addresses, and checks to see if they are correct. Then, let it run for a few days, and hopefully when you come back, it will have found your seed!