P deficiency?

I cut off the single blade leaf but not sure what the issue is.
First time grower

Yup! Phosphorus deficiency. Hit with a dose of bloom nutrients.

Don't hinge your grow on that leaf...it's at the bottom of your plant, it's a single blade leaf...all of which means it's super old (being it was one of your first leaves on the plant). Don't sweat it in terms of this. More importantly is: What are you feeding, what are you growing in and is the plant in flower now? The devil is in the details.

Growing in compost soil, still in veg..
recently gave it mg then compost tea 2 days later.
am i burning them.
i have banana peel tea processing now.

It's hard to say if you're burning them...but it doesn't look like it. I'm guessing the soil is your own, or no...what can you tell us about it ? By giving it Mg, did you do that using Epson Salt, or?...and how did you apply it, via spray or into the pot? If it were me, I would think phosphorus wouldn't be an issue, on average...unless you were in flower or your pH is whacked. I would lean more towards an Mg shortage, which would most likely clear right up if you sprayed with Epson Salt. If the plants did improve, then you'd know you need to be adding more Mg into your feed. Never the less, try eliminating things, one at a time. Don't throw the kitchen sink at her...if she's in veg, you have time to figure it out. Good luck friend.

New lower leaves gave mg from Epsom salt. And yes its my own compost soil .. ph is around 6.6. I have been feeding via foliar and directly to soil.. just added some banana tea last night for potassium calcium and more mg

Compost from what? Compost is usually used as an ingredient in soil along with other things like worm castings, peat, coco, perlite, rice hulls, etc... and other amendments like lime, bone meal, guano, azomite, rock phosphate, etc... to make a balanced soil. That compost you're using may not have everything the plant needs in adequate quantities and that banana peel tea may not provide what the plant needs.

If you're trying to grow organic you should look through the organics section before you start your next grow. There's quite a bit of information there regarding mixing up a decent soil mix. That's all I have to offer. Without knowing anything about what's in that compost anything related to the issues with the leaves would just be a guess.

Good luck.