Time inconsistency

Hi- I’m totally new to cubase, or any type of musical program. I don’t know any of the… what should I say, professional words in the program at all.
I searched youtube to learn how to record my vocals and I got there in an amateur way. But there’s a really annoying problem- between the inst and the record, the time won’t match. What I mean is, during the recording, I sing to the instrumental and the speed matches. But when I check what I recorded, the instrumental is always a little slower or faster, anyway it doesn’t match! So I just use this to control the speed of the recorded track.

(the red circle)

I’m terribly afraid that I’ve done something wrong. I don’t think it used to be like this the first time I bought this.
What’s the problem? Why is it happening? and how do I fix this?
I’m really desperate for an answer.

You will need to select a lower buffer size to lower the latency. Which audio Interface are you using?

Which Cubase?
Which interface?

I;m using the Scarlett solo (2nd generation) and Cubase Elements 9… how do I select a lower buffer size?
I’m sorry- I know nothing. I’m a total outsider in this area!