Drop 4U if you think you won't get at least 70. If you don't get 70 it probably won't count.
Keep in mind 70 is pretty hard to get and you can out scale 4U by doing well in other things anyway...
If private school then you may have to speak to the head master/principal.
Edit: Nevermind...OP they definitely can't force you in a public school. Do what Bilt said
Keep all for now. You're doing so well in all of them you're obviously coping fine.
Wait until first assessments or something and then decide to drop one based on how you felt so far.