That's not terrible. I pay something like $140/mo for 1gbps (in reality I've never seen speeds >300mbps) with no data cap. $100 for ~100mbps with no data cap is reasonable to me.
If you get a good tech they will help you, you may get a dud, in which case you simply have to call them up and work the system again.
It's totally doable, I've done it dozens of times at every dwelling I've inhabited. I'm currently on their 1GB plan, and I do get 1.4Gbps down (they recently upped their provisioning rate, and with a newer modem with 1 2GB link on it, with a suitable router [I run the UDM Pro] it works).