While traditional proposals may be similar to kiddushin, they have no halachic ramifications regarding kiddushin. (For starters the ring has to be given with intent to be makdish the women.)
What actually has halachik ramifications is the actual verbal agreement to get married (or in this case checking the box). According to most poskim, that is a binding halachik agreement that must be kept unless BOTH sides agree to revoke it. (Similar if he would verbally agree to sell you something at a certain price, neither of you can back out if the other wants to go ahead with it.) This has MASSIVE ramifications when it comes to broken engagements where only one side wants to break it.
The irony is the legalism about whether or not you had jurisdiction over him and your username. Halchically it is him having jurisdiction over you not visa versa, it would sound more like you should have run the legalism.