A quick update to my earlier reply that I thought might be helpful for u/cobalt-ambedo, u/demosthenesss and OP u/Mrs_WorkingMuggle.

I was fortunately able to login in after multiple tries, setup an account, and purchase my iBond. I noticed that the site was MUCH easier to access after about 1 am Eastern Time (had to stay up late for this). Not sure if it's because traffic to the site is lower, or due to some schedule maintenance they did around midnight Eastern ... but the site worked much faster.

You might want to give the overnight hours a shot if you're able. There's only one night left to try it (unless you're in a position to do it now). But worth a shot.

Good luck to you!