saijeuga eobseulkka bwa kuponeul batjamaja baro jumunhaesseo.

-을까 봐 means for fear that..., in case..., or because I was worried that....

So 사이즈가 없을까 봐 means:

• because I was worried they might not have my size
• in case my size would be unavailable

It expresses a concern about a possible future situation.

Structure:

• 있다 → 있을까 봐
• 없다 → 없을까 봐
• 늦다 → 늦을까 봐

In this sentence, the speaker ordered quickly because they were worried the right size might sell out or not be available.

These have different meanings.

• 없어서 = because there wasn’t any / because it didn’t exist
• 없을까 봐 = because I was worried there might not be any

So:

• 사이즈가 없어서 주문했어 would sound illogical, because it means I ordered because there was no size
• 사이즈가 없을까 봐 주문했어 means I ordered because I was afraid my size might be unavailable

The speaker is not saying the size was already gone. They are saying they acted quickly out of concern.

Because 없다 usually takes the subject marker 가/이, not the object marker 를.

So:

• 사이즈가 없다 = there is no size / the size is unavailable
• not 사이즈를 없다

In Korean, 있다 and 없다 often describe existence or availability, so the thing that exists or does not exist is marked with 이/가.

Examples:

• 시간이 없어 = I don’t have time
• 자리가 없어요 = There are no seats
• 원하는 색이 없어요 = They don’t have the color I want

Here, 사이즈가 없을까 봐 means for fear that the size might not be available.

-자마자 means as soon as.

So:

• 쿠폰을 받자마자 = as soon as I received the coupon

This grammar emphasizes that one action happened immediately after another, with almost no delay.

Structure:

• verb stem + 자마자

Examples:

• 집에 오자마자 잤어 = As soon as I got home, I slept
• 연락을 받자마자 출발했어 = As soon as I got the message, I left

In your sentence:

• 쿠폰을 받자마자 바로 주문했어 means the speaker ordered immediately after getting the coupon.

They are similar, but not exactly the same.

• 받자마자 = as soon as I received it
• 바로 = right away / immediately

Using both together adds emphasis:

• the moment I got the coupon, I ordered immediately

So yes, there is some overlap, but it sounds natural. Korean often uses both to make the immediacy feel stronger.

Compare:

• 쿠폰을 받자마자 주문했어 = I ordered as soon as I got the coupon
• 쿠폰을 받자마자 바로 주문했어 = I ordered immediately as soon as I got the coupon

The second one feels a bit more emphatic.

That is very normal in Korean.

Korean often puts:

1. the reason or background first
2. the main action later
3. the final verb at the end

So this sentence is structured like:

• 사이즈가 없을까 봐 = because I was worried there might not be my size
• 쿠폰을 받자마자 = as soon as I got the coupon
• 바로 주문했어 = I ordered right away

This order is natural in Korean because details like reason, time, and manner usually come before the main verb.

A very literal breakdown would be:

• Worried there might not be my size, as soon as I got the coupon, I immediately ordered.

주문했어 is the casual/informal polite-down style, often used:

• with friends
• with people younger than you
• in diaries
• in casual conversation

주문했어요 is the polite version.

So:

• 주문했어 = casual
• 주문했어요 = polite

The grammar and meaning are the same. Only the speech level changes.

You could say:

• 사이즈가 없을까 봐 쿠폰을 받자마자 바로 주문했어요.

That would be the polite equivalent.

Yes, the subject is omitted because Korean often leaves it out when it is obvious from context.

In this sentence, the person who is worried and the person who ordered are the same person: I.

So the full idea is:

• I was worried there might not be my size, so I ordered immediately as soon as I got the coupon.

Korean does this very often. Instead of repeating I, the sentence just focuses on the important information.

In natural usage, it usually means my size might be unavailable or the size I need might be sold out.

Even though 사이즈가 없다 literally looks like there is no size, in shopping contexts it commonly means:

• they don’t have the size
• the size is out of stock
• my size might be gone

Context does a lot of work here. A Korean speaker would usually understand this as concern about stock availability, not literally that the product has no size system.

Yes, but the nuance is different.

• 사이즈가 없을까 봐 = because I was worried there might not be my size
• 사이즈가 없을 것 같아서 = because I thought there probably wouldn’t be my size

So:

• -을까 봐 focuses on fear/worry
• -을 것 같아서 focuses on expectation/impression

If you want to emphasize anxiety or caution, -을까 봐 is better.

Yes, definitely.

This part suggests:

• the speaker received a coupon
• then immediately placed the order
• the coupon likely gave them a reason or opportunity to buy right away

Combined with 사이즈가 없을까 봐, the full nuance is something like:

• I didn’t want to wait, because I was worried my size might be gone, so the moment I got the coupon, I placed the order right away.

So the sentence gives two motivations at once:

1. fear of missing the size
2. the coupon arrived, giving a good chance to buy immediately