Act 2:21 Shall call on (epikalesetai). First aorist middle subjunctive of epikaleo, common
verb, to call to, middle voice for oneself in need. Indefinite relative clause with ean and so subjunctive, punctiliar idea, in any single case, and so aorist.
A.T. Robertson.
ἐπικαλέω. fut. mid. ἐπικαλέσομαι; 1aor. ἐπεκάλεσα, mid. ἐπεκαλεσάμην; pf. pass. ἐπικέκλημαι; pluperfect mid. ἐπεκεκλήμην; 1aor. pass. ἐπεκλήθην; (1) active, in speaking of a person call, name, give a surname (MT 10. 25); passive be called, be named (AC 1. 23); (2) passive with ὄνομα (name), idiomatically, denoting that one person belongs to another whose name is attached to him ἐπικαλεῖσθαι τὸ ὄνομά τινος ἐπί τινα literally have someone 's name called on someone, i. e. belong to, be the person of (AC 15. 17); (3) middle, as a legal technical term for appealing to a higher court appeal, call or summon as witness (2C 1. 23);
(4) middle, as invoking God' s name in prayer call on (AC 2. 21) Analytic Lexicon of the New Testament.
I wouldn't call invoking God's name for help as worship.
Worship is defined as...
Jn 4:23-24 23 But the hour cometh, and now is, when the true worshipers shall
worship the Father in spirit and in truth:for the Father -- seeketh such to
worship him.
24 God is a Spirit:and they that
worship him must
worship him in spirit and in truth.
Jn 4:23 . The true worshippers (hoi alethinoi proskunetai). See
1:9 for alethinos (genuine). Proskunetes is a late word from proskuneo, to bow the knee, to worship, A.T. Robertson
προσκυνέω. impf. προσεκύνουν; fut. προσκυνήσω; 1aor. προσεκύνησα; (1)
from a basic sense bow down to kiss someone 's feet, garment hem, or the ground in front of him; (2) in the NT of worship or veneration of a divine or supposedly divine object, expressed concretely with falling face down in front of someone worship, venerate, do obeisance to; (a) toward God (MT 4. 10); (b) toward Jesus (MT 2. 2); (c) toward the devil and demons (MT 4. 9; RV 9. 20); (d) toward idols (AC 7. 43); (e) toward human beings as given or claiming to have divine power or authority (RV 3. 9; 13. 4 b)
Analytic Lexicon of the New Testament.
A. Verbs (Worship)
1.
proskuneo (προσκυνέω, 4352), "to make obeisance, do reverence to" (from pros, "towards," and kuneo, "to kiss"), is the most frequent word rendered "to worship." It is used of an act of homage or reverence. (Vines)
Thus epikaleo and proskuneo are not the same word nor have the same meaning.