I'd like to address the core concern directly here:
I have the offer letter but the salary is way more than what i had in
mind - like 25% more than what I had expected.
This is absolutely nothing to worry about, especially in a high-demand field, for one simple reason: 25-50% isn't really that much. And don't take my word for it!
Computer Systems Analysts [simple example, requiring only a bachelor's]
The lowest 10 percent earned less than $49,950, and the top 10 percent
earned more than $122,090. [emphasis added]
Note that the top range is more than twice the bottom range, and note the words "more than". If you got an offer for $160,000, you'd probably be in the top 5 for that position, but 1 out of 20 people are in the top 5% so that's hardly that weird! Note that this range increases as you move up in positions, for example:
Computer and Information Research Scientists [noted as requiring a
higher level degree)
The lowest 10 percent earned less than $57,220, and the top 10 percent
earned more than $151,900.
The other thing to be aware of is that, in a field where demand by employers is greater (at least temporarily) than qualified/suitable applicants, prices can jump dramatically overnight!
As something I personally experienced, a local education company in my area increased their starting wage for programmers 25% from one week to the next, putting them about 20% above what other employers post as a starting wage in the same city. The reason? They are expanding and there is so much competition from other employers (insurance companies, banks, and other education companies) that they complain that they can't find enough people even if 100% of current applicants were actually hire-able!
In other words: enjoy your windfall, a mere 25% increase in salary is great for you personally and is small potatoes to business in high-demand high-profit-margin industries. It's normal, and you are at no more risk of being conned into an organ harvesting scheme than you would be if they offered you a lower salary.
Do a good job, network well, build your network, and enjoy your new opportunity. Markets are fickle, so just make sure you contribute appropriately to your emergency savings fund, retirement, etc!