Yes, you are still eligible for a free seat next year if you appear for ECET again, as long as you meet the following conditions:

• You do not join the current allotted college officially by submitting original certificates and paying full admission fee.

• You do not freeze the seat or attend any classes officially under this admission.

• When you appear for ECET again next year, you must go through the entire counselling process again from the beginning.

Since you only self-reported online and did not submit originals, it's considered as not completing admission. That means you haven’t utilized your free seat quota yet, and you can still compete for a convener quota (free seat) next year.