Whats up, your proposed cycle so far is ok. I would personally adjust the deca to Test ratio.
If you insist on running 300mg deca, i would bump up the Test to 400mg or 450mg even, because of nandrolones binding affinity to the androgen receptor.
Nandrolone is binding 1.5x stronger to the receptor than Testosterone. So a ratio of 1.5:1 test:deca is optimal.
Your Dbol is dosage is perfect imo. You def will feel the effects and encouter min. Sides. (Ran the same dosage)
Proviron or masteron is always a nice add on to a deca cycle, because of the added DHT in your system. Nandrolon does lower your DHT because of its metabolite DHN, thus lowering your libido, mood, energy, your Willy says goodbye and so on. DHT, DHN will be battle for the place at your receptor, so in my experience, i always kept my DHT high, when running deca or npp (not so much NPP but on deca for sure).
I would bump up your cycle length to 15 weeks even 20 weeks for the sake of it because, for deca to fully kick in and you fully get all of its effects 8 weeks have passed already and your cycle is almost over.
And bro, you are definitly not at 20% lmao. You are probably at like 12-14% BF(judging from your pic of course), but again I am also just guessing here.
Anyway, hope your found this helpful

. I am open for any sort of correction if I Made some Mistakes in my comment