You're still inside of your warranty. First, take a few pictures from a couple of different angles (with good lighting at your back.) Then, take out a sheet of paper and put today's date on it and a note that you called the builder. Then, make notes of what they told you. Follow up that call with a letter, certified mail, return receipt. Keep the receipts! Add this 'info' to your sheet of paper, dating and timing what and when you do 'whatever'.
At some point, the builder will come or call. Again, make notes on this paper. Assuming all goes well, a repair/replacement is done. Add this to your notes too. You see what's happening here? You're keeping a log of EVERYTHING that's transpiring so that in case 'he' drops the ball, you have a record of what you did. Feel free to add other 'issues' to our conversation(s) and letter(s) as you go. Again, document everything.
Assuming all goes well, ask the builder for a new, WRITTEN warranty, for whatever 'new/fixing' work he does. (It should be 1 year as with the 'original workmanship'.) Make that a big point. He may 'press' you on not doing it but that's where your Real Estate Attorney comes in. You did have one for your closing and such, right? If not, you may end up getting one anyway if you feel you're being 'cheated'. (I'm a big fan of spending a few hundred $$$ to 'retain' an attorney during the buying/building process to protect YOUR interests when you're spending possibly 100's of 1000's of $$$ on a new home. 'nough said 'bout that.)
Dependin, seams can be fixed but w/o seeing the extent of the damage, it's hard to say. If you know the EXACT type of flooring you have, you can ctc. the mfgr. or a local retailer to get a copy of the Installation Instructions and the Warranty. This may tell you more. For example, maybe the mfgr. won't warranty their floor IF it was installed on, say, OSB. This way, if you know what you have in the house, you'll know if you might be calling him back in a few months for the same problem! Then, you can 'point out' the Instructions and/or the Warranty. At worst, you can give this info to your Attorney, along with the specs for the house. (This would be useful 'ammumition' for the Attorney.)
Maybe others have more to add. My best to ya and hope this helps.
PS: After this afternoon, I won't be back until Tuesday morning but others will be 'around' ...