Polytechnic

Before answering your question, let me introduce a little bit about myself.
I am also a diploma holder in ECE of 2009-2012 batch from Guru Nanak Dev Co-Ed Polytechnic, Delhi. I am a mediocre person im studies.
So, when I was in your situation (what to do after completion of diploma), I did the following:
Gave interviews (both on campus & off campus), and failed miserably as they were not core EC companies and I was not prepared for this.
I filled many application forms for LEET in the northern region of India (Rajasthan board, UP board, Himachal board, Punjab board, etc. and of course, GGSIPU, Delhi) in an attempt to get a seat in any of these colleges for B.Tech.
Side by side, prepared for any govt. vacancies suitable my discipline.
When the above 3 points were hovering in my mind, I gradually lost interest in my semester studies and couldn't schedule how to study simultaneously.
Impact of these actions:
I couldn't performed better in last semester.
I ended up with not so decent rank in the LEET exams.
I was depressed and looking for motivation to make a comeback.
What happened afterwards?
I developed my interest slightly from Electronics to Computers and decided to choose my major as Computer Science.
I miraculously got a CSE seat in MAIT (GGSIPU), despite my rankings.
I am about to be a graduate from this awesome institute and planning for higher studies.
You see the point I am trying to make, I hated programming during my diploma days and now I am preparing to do research (M.S.) in one of the computer science field. So, yes, you should do what you love and love what you do. It took me a time to realize this later in my life. However, I am equally passionate about Electronics till now.
Advice for you:
If you can afford to manage the academic fee for B.Tech, then you should definitely do it. Otherwise, you can take educational loan and pay back later when you have job.
You can drop a year to prepare well (trust me, it could be worthwhile) if you aren't sure of good college. Many of my classmates have done this and are in good colleges with their desired branch.
Search for a job, there are plenty of private jobs for CS background. You can side by side prepare for LEET, if you can manage and also gain experience.
You can prepare for a govt. job (DRDO), although there is much scarcity of govt. jobs for CS.
You can enroll for part time B.Tech in DTU and others. You can search for the institutes that provides them. In that case, you need to have a job.

BCA is much better as compared to B.Sc. Because, B.Sc is a general course whereas BCA is a technical course. Getting a job after BCA is relatively easy as compared to B.Sc. As you are not able to pursue B.Tech, then you'll have to work much harder on developing skills and knowledge while pursuing BCA in order to achieve a good career with nice salary package. If you want to learn programming languages which you will be studying in your BCA course then you can check out this app which is specially designed and developed for BCA students. It has programs and assignments of languages like C, C+ and Java with their outputs. You'll be studying these languages in your 3 years of BCA. https://play.google.com/store/apps/details?id=technark.bca_courprogramming.