The end date is a target, not a deadline
Your campaign ends when the budget is spent. The end date tells Sprizzy how fast to spend it.
If delivery is slower than expected, the campaign can run past the date you chose, because there is still money in it. If delivery is faster, it can finish early.
Why you can only choose a few days
Google Ads requires a campaign to spend at least $5 per day. That means your budget decides the longest schedule available. A bigger budget allows a longer run, and the campaign builder shows you the maximum for the budget and locations you pick.
Adding funds to a running campaign
Adding funds without moving the end date means the same number of days has to absorb more money, so the campaign spends faster. If you want the pace to stay the same, extend the end date when you add the funds.
Campaigns that stop on their own
If a campaign runs for several days without delivering any views, Sprizzy ends it and moves the unspent budget to your account balance, so the money is not left sitting in a campaign that is going nowhere. You will get an email when this happens.
What to do next
To change dates, open the campaign menu and choose Edit Campaign. To stop a campaign now and get the unspent money back, read How do I end a campaign early?.