Thank you both !
Still USA is USA ... i would like to try it for sure and maybe live there, but on the other hand it's not too important that I would give up my unfinished bachelor degree just to move quickly to USA without having problems with later immigration to U.S.
So I don't know yet whether it is good reason to keep gc if ain't definitively decided to live permanently in the U.S. If I had gc and wouldn't move to USA in future I also wouldn't like to risk my prospective pure tourist travels USA.
First, don't feel like you have to committ to live in the US forever. I think it's perfectly ok to get your GC, try to live in the US for a few years, and see if it is the right thing for you. You never really know what kind of life you will want 5-10 years from now. Maybe you will want to live in the US all the time, maybe you will want to live in the US and spend the summers in Europe, maybe you will want to return to Europe permanently.
What is known is that it's really hard to obtain permanent resident status in the US. Even if you have a Ph.D. degree from a top American university, US employers will usually first hire you on a H1B visa, and then sponsor you for a green card 3-4 years later if you do well. The process will then take 1-3 more years before you finally get your green card. People with regular university (B.S.) degrees have been waiting for 3-6 years, even after finding an sponsoring employer.
On the other hand, you can get your green card in a few months.

You will always have your European citizenship to fall back on. And after 5 years as a permanent resident you can apply for US citizenship.
Living here (say in San Francisco or New York) can definitely be a great experience. But I think in your situation you should
think about your education first. The US is full of opportunities, and these opportunities are the better for young people who have degrees from US colleges; the opportunities are really great for young people who have degrees from top US colleges.
What you can do is transfer from your university to a US college. It will be very very competitive to transfer to a school such as Stanford, depending on your educational accomplishments. It will be easier to transfer to a state school such as UCLA, University of Illinois at Urbana-Champaign, or University of Texas at Austin.
Unfortunately, the transfer application deadlines are now largely over. So you would have to apply for transfer admission next year. What you can do in the meantime is enroll in a community college (or similar college) for a year, to prepare for applying as a transfer to a school such as UCLA next year.
It will be much easier to be admitted and to obtain financial aid as a permanent resident. Permanent residents are treated as US citizens almost always.
Here are some more details if you decide to do it:
If you move to California (or another state) as a permanent resident, you will be considered a state resident, and will be eligible for significantly lower tuition at state schools (e.g. at UCLA you would avoid the $19,068/year out-of-state tuition).
Check the residence requirements for state schools before you make a plan where to move. A good starting point for your plan is to move to California, establish California residency, and then apply for transfer to University of California schools (as well as private schools such as Stanford, Cornell, etc). University of California has a number of campuses, from very good ones such as UC Berkeley, to good ones such as UCLA, to ... more relaxed ones.
You have to decide if you want to turn your life upside down and transfer to an American university and go for this opportunity. A lot depends on where in Europe you are and in what kind of university.
- For example, if you are a top student at TU Berlin and want to apply for a Ph.D. afterwards, it doesn't make sense to transfer. You are likely to be accepted into very good Ph.D. programs in the US after you graduate from TU Berlin anyway.
- But if you are a student at a regular state university in Poland (just an example) and you want to work for an interesting company after graduation, transfering could provide great opportunities for you.
So, think about education first, and keep in mind that having a green card really improves your opportunities for education in the US. Good luck!