Hey D. I am so sorry to hear that your introduction to IOTA was tainted by this misfortune! I hope that you are able to recover your IOTAs, and that you are still excited to participate in the future of the Internet of Things!
Real quick, I want to confirm something: Did your friend send the IOTAs to your seed, or did they send IOTAs to an address that you generated after logging into the wallet using your seed?
If they sent IOTAs to your seed:
This is unfortunately not a recoverable situation, because what your friend actually did was send IOTAs to an address that has the same value as your seed.
The only way to recover the funds would be to find the seed that can generate that address, which is virtually impossible (this is by design; otherwise, anyone could steal IOTAs by guessing other people's seeds!).
If they sent IOTAs to an address generated using your seed:
Depending on the version of the IOTA wallet that you are running, there is potentially some good news here.
Since (I think) version 1.0.3, the wallet will not let you enter seeds with invalid characters (see here for more info), and it will warn you if your seed is not exactly 81 characters (hopefully, if this warning did appear, you took note and double-checked that you entered the seed correctly!).
So, depending on what you had in your clipboard at the time, it's probable that your seed is not completely random (e.g., if you had a URL or some text with punctuation in it, the wallet wouldn't have let you use that as a seed).
The first thing I would do is look at the seed you wrote down and note any characters that might be ambiguous. E.g., if the letter is smudged, or maybe you misread an "I" as an "L", etc. Try some different variations, and see if you can find the seed that you typed in.
There's also a possibility that you just mistyped one or more characters. This will be a lot harder to recover from because it's impossible to know which characters are correct and which are incorrect.
This is where you might need to turn to a "seed recovery" service (somebody who's written a program that can guess different combinations of typos based on a known seed). I don't think any exist at the moment, but your IOTAs aren't going anywhere, so hang onto your seed — at some point there should be somebody who can help!