Too much pressure

Looking for some help - I installed two new baseboard units yesterday. I connected them to an existing baseboard unit in another room. I turned the water back on - bleed the air out of the line - and everything seemed fine. I went down to the basement an hour later and water was coming from the release pressure value. I looked at the pressure gauge and it was in the red. I shut off the system and drained the water which reduced the pressure. I thought maybe air was trapped in the system (could be - I am not sure)

I thought maybe that I broke the expansion tank - it seems fine - the knock is different from the top to the bottom.

Any thoughts on what it might be?