I was having this issue for 2 months!
My heart fears started a few months ago when I all of a sudden realized "wait, my dad had heart disease, why am I so worried about cancer and other things when I have a big chance of having heart disease because of family history?" That's when I started obsessively checking my heart rate, and it was always 82-88 (which is high for me).
I scheduled a EKG with a cardiologist and he did it and listened to my heart too and said it was normal. He said in two weeks if I want I can have a stress test done, even though he didn't think i needed it. For those two weeks, I again kept checking my heart rate and it was still in the 80's.
I got the stress test done last week, and the doctor said all looks good and normal, and every day since I've been checking my heart rate and it's been 66-70.
My point is, even when we have an inkling of anxiety, I think our sub conscious works overtime even though we may not feel like it is. But after it all calms down, everything goes back to normal.
So maybe you built up a lot of anxiety over this and that's why your HR is high; especially when you're checking in and probably thinking to yourself "OMG I hope it's not high" then boom it's high because like someone else said, your nervous system kicks in.
If you've had an Echo AND EKG, you're fine... something would have popped up! Especially with the echo... and I'm assuming they checked your BP too along with those tests, so if all is normal, all is normal.. sometimes even though we may feel like we're calm and not anxious about it anymore, it can take our physical body weeks to catch up because of the anxiety we put it through.