You can make your sujood longer using below invocations proven from sunnah.
Abu Musa al-Ash’ari (RAA) narrated, “The Messenger of Allah (ﷺ) used
to supplicate,'Rabbi-ghfir-li Khati 'ati wa jahli wa israfi fi `Amri
kullihi, wa ma anta a'lamu bihi minni. Allahumma ighfirli khatayaya wa
'amdi, wa jahli wa jiddi, wa kullu dhalika'indi. Allahumma ighrifli ma
qaddamtu wa ma akhartu wa ma asrartu wa ma a'lantu. Anta-l-muqaddimu
wa anta-l-mu'akh-khiru, wa anta 'ala kulli shai'in qadir.' “O Allah,
forgive me my faults, my ignorance, my immoderation in my concern. And
you are better aware (of my affairs) than myself. O Allah, grant me
forgiveness (of the faults which I committed) seriously or otherwise
(and which I committed) inadvertently and deliberately. All these
(failings) are in me. O Allah, grant me forgiveness from the faults,
which I did in haste or deferred, which I committed in privacy or in
public and you are better aware (of them) than myself. You are the
First and the Last and over all things you are Omnipotent.” Agreed
English reference : Book 16, Hadith 1606
Arabic reference : Book 16, Hadith 1563(2819)
Allaahumma laka sajadtu wa bika 'aamantu, wa laka 'aslamtu, sajada
wajhiya lillathee khalaqahu, wa sawwarahu, wa shaqqa sam'ahu wa
basarahu, tabaarakallaahu 'ahsanul-khaaliqeen.
O Allah, to You I prostrate myself and in You I believe. To You I have
submitted. My face is prostrated to the One Who created it, fashioned
it, and gave it hearing and sight. Blessed is Allah, the Best of
Reference: Muslim 1/534
Allaahum-maghfir lee thanbee kullahu, diqqahu wa jillahu, wa 'awwalahu
wa 'aakhirahu wa 'alaaniyata hu wa sirrahu.
O Allah, forgive me all my sins, great and small, the first and the
last, those that are apparent and those that are hidden.
Reference: Muslim 1/350.
Allaahumma 'innee 'a'oothu biridhaaka min sakhatika, wa bimu'aafaatika
min 'uqoobatika wa 'a'oothu bika minka, laa 'uhsee thanaa'an 'alayka
'Anta kamaa 'athnayta 'alaa nafsika.
O Allah, I seek protection in Your pleasure from Your anger, and I
seek protection in Your forgiveness from Your punishment. I seek
protection in You from You. I cannot count Your praises. You are as
You have praised Yourself.
Reference: Muslim 1/352.