Yeah, I know how you feel when the score says something completely off. I have a pretty decent rhythm but I did go through it a few times just so I was absolutely sure I am not telling lies because "the score never lies"

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I am thinking this real time, so it may not be the most optimal exercise but if you want to work on your rhythm, take a metronome, set the tempo to 40-60BPM 4/4 and pick/strum/clap/sing/snap your fingers/tap your foot/etc. first on quarter notes, then go eights, then go 16ths, then go triplets. I think this is where most of players would stop and it is enough for a big % of the music in the world.
Oh and let's take this a bit further. I assume you're practicing this exercise with strumming. Mute the strings with your fretting hand, and do the above. Once you become consistent and you develop really good 16th notes, you might want to work on your accents as well (I would say most people connect this to funk music - I also saw variations of this exercise in multiple books and videos regarding funk rhythm guitar).
You play 16th notes but every bar you accent one of the "1 e & or a".
1 e & a
2 e & a
3 e & a
4 e & a
1
e & a 2
e & a 3
e & a 4
e & a
1 e
& a 2 e
& a 3 e
& a 4 e
& a
1 e &
a 2 e &
a 3 e &
a 4 e &
aAnd you keep repeating this until you can talk to other people and still doing it on time

. I am faaaar from reaching that point but one day, I'll get there!
Oh and another tip:
If you want to check how accurate your rhythm is to an extreme, you might want to record yourself to a click track. Then zoom in the waveform (any audio editing software will do, Audacity as well) and you will see if metronome and your strum align. And believe me, this will not make you a robot. Once you "lock it in", your groove gets better as well. But it will allow you to go on some "dodgy rhythmic journeys and still land on the beat when the chorus starts" (sorry, a terrible explanation)
