It's only one possible interpretation, though, there may be equally valid other readings.
When it's the construction
~neg-Vと。
(end of sentence)
the likelihood of alternative interpretations is vanishingly small.
There are twelve such example sentences in WWWJDIC.
あのプロジェクトについて彼を本気にさせないと。
We have got to get him to take that project seriously.
うちの電話は故障だ。修繕してもらわないと。
Our telephone is out of order so I shall have it repaired.
どういっても七時までにいかないと。
However we go, we must get there by seven.
もう行かないと。
Got to go now.
恐縮だが、残業してもらわないと。
I'm afraid that you have to work overtime.
金をためるには出費を切りつめないと。
We must cut our expenses to save money.
今頃言うなんて遅いよ。事が起こった時に言わないと。
Don't come to me now with that. You should have said something when it originally happened.
昨晩は遅くまでがんばって働いたから、もし可能なら、お昼をとった後少し眠らないと。
I worked hard till late last night, so I'll have to catch some z's after lunch if it's possible.
生卵はだめ。調理しないと。
I can't eat a raw egg; it must be cooked.
電池を入れ替えないと。
It needs new batteries.
髪を整えないと。
I've got to fix my hair.
彼にお金を返すのを忘れないようにしないと。
I've got to remember to return this money to him.
Incidentally the second example is also a form often used when people talk to themselves.