Chciałam zrobić zwrot tej sukienki, ale nie miałam przy sobie paragonu.

Because this is 1st person singular past tense: I wanted / I had.

In Polish past tense, the verb also shows the speaker’s gender:

• chciałam, miałam = said by a woman
• chciałem, miałem = said by a man

So a male speaker would say: Chciałem zrobić zwrot tej sukienki, ale nie miałem przy sobie paragonu.

This is about aspect.

• zrobić is perfective: it suggests a completed, one-time action
• robić is imperfective: it suggests an ongoing, repeated, or general action

Here, returning the dress is seen as a single complete action, so zrobić fits well.

So:

• chciałam zrobić zwrot = I wanted to make/complete a return
• chciałam robić zwrot would sound less natural here, because it suggests being in the middle of doing the return rather than simply wanting to carry it out

Yes, you can absolutely say zwrócić tę sukienkę, and many learners will find that version simpler.

Both are understandable:

• zrobić zwrot tej sukienki = make a return of this dress
• zwrócić tę sukienkę = return this dress

A very natural alternative is: Chciałam zwrócić tę sukienkę, ale nie miałam przy sobie paragonu.

About zwrot itself:

• after zrobić, zwrot is in the accusative
• for a masculine inanimate noun like zwrot, the accusative looks the same as the nominative, so you still see zwrot

Because tej sukienki depends on the noun zwrot.

The pattern is:

• zwrot czego? = return of what?
• answer: tej sukienki

That means tej sukienki is in the genitive.

Compare:

• zrobić zwrot tej sukienki = make a return of this dress → genitive
• zwrócić tę sukienkę = return this dress → accusative

So both are correct, but they follow different grammar.

Because ta changes form depending on the case.

For ta sukienka:

• nominative: ta sukienka
• accusative: tę sukienkę
• genitive: tej sukienki

In this sentence, the phrase is tej sukienki because it is in the genitive after zwrot.

Because in Polish, the object of a verb often changes to the genitive after negation.

Compare:

• miałam paragon = I had the receipt
• nie miałam paragonu = I didn’t have the receipt

This is very common with mieć:

• mam czas → nie mam czasu
• mam bilet → nie mam biletu
• mam paragon → nie mam paragonu

So paragonu is genitive singular.

No. It is in the genitive because of nie miałam.

The phrase przy sobie is just a fixed expression meaning on me / with me / on my person.

So the structure is basically:

• nie miałam paragonu = I didn’t have the receipt
• przy sobie adds the idea with me / on me

In other words, przy sobie does not force paragonu into that case.

Przy sobie means with oneself, often in the sense of physically on you or on your person.

So:

• nie miałam przy sobie paragonu = I didn’t have the receipt on me / with me

Yes, ze sobą is also possible:

• nie miałam ze sobą paragonu

The difference is small:

• przy sobie often sounds a bit more like on my person
• ze sobą is a more general with me

Both are natural.

Usually paragon means a shop receipt, especially the cash-register receipt you get after buying something.

It is not exactly the same as every possible English use of receipt.

Useful related words:

• paragon = store/till receipt
• rachunek = bill/check, sometimes receipt depending on context
• faktura = invoice

In a clothing store return situation, paragon is exactly the word you would expect.

Because the speaker is describing a past situation.

The meaning is:

• I wanted to return the dress
• but I didn’t have the receipt with me

So both the wanting and the not having happened in the past.

If you wanted to express a present polite request instead, you would use something like: Chciałabym zrobić zwrot tej sukienki. That means I would like to return this dress.

No, Polish word order is fairly flexible.

The given version is natural and neutral: Chciałam zrobić zwrot tej sukienki, ale nie miałam przy sobie paragonu.

But other orders are also possible, with slightly different emphasis, for example:

• Ale nie miałam przy sobie paragonu.
• Paragonu nie miałam przy sobie.
  This emphasizes the receipt
• Nie miałam przy sobie paragonu.
  This is a very neutral statement

Polish often changes word order to highlight what is most important or contrastive.

A very common polite version would be:

Chciałabym zwrócić tę sukienkę, ale nie mam przy sobie paragonu.
if the speaker is female

or

Chciałbym zwrócić tę sukienkę, ale nie mam przy sobie paragonu.
if the speaker is male

Why this sounds more polite:

• chciałabym / chciałbym = I would like to
• present tense nie mam can fit a current shop interaction better than the past nie miałam

So the original sentence sounds like a past narrative, while this version sounds like something you might say directly to a shop assistant right now.