Sure, you can check in any time inside 45 days but as you found out you may not get the check in time you wanted. An earlier slot may open sometime inside those 45 days, but unlikely. The chosen check in time may not matter much - it is rarely enforced.
Your status should update to D on Friday - it may or may not make onto the ship when they print the Seapass cards for your sailing Friday. If not, do as @Ourusualbeach suggested.
Starlink has no affect on the WiFi inside the ship which is the issue in the theater. We tried to use it almost every night on the TA - we could never get it to work reliably. Folks sailing Jewel are very lucky in that she is one of few ships on which the speeds have not been throttled to the usual 4Mbps and can be over 100Mbps.