That is a different letter (notice the little hat above) which represents a different sound than /a/. There's also "î" which represents the same sound. Unfortunately, if you are a native English speaker, you don't have that sound in your language, so it might be difficult to recognize and pronounce it.
The TTS here is quite good, but here are two examples that might help you differentiate between it and /u/ (though the quality is not great):
https://forvo.com/word/ro/lun%C4%83/#ro (moon or month)
As a fun fact: before an orthographic reform in '93, the spelling of: sunt, suntem, sunteți (I am, we are, you (pl.) are), was sînt, sîntem, sînteți, which suggests that, even for Romanian speakers, there's a grey area between /î/ and /u/.