Saya menyemat kelim itu kalau-kalau jahitannya longgar.

Menyemat comes from the root semat, and here it means to pin, to fasten, or to secure with a pin.

In a sewing context, it usually suggests attaching something temporarily or carefully fixing it in place. So in this sentence, menyemat kelim means something like pinning the hem or securing the hem.

The prefix meN- makes it an active verb:

• semat = the root
• menyemat = to pin / to fasten

Kelim means hem.

In sewing, a hem is the folded edge of cloth that is sewn down. So kelim itu means that hem or the hem.

Depending on context, kelim can refer to:

• the finished edge itself
• the folded part of the fabric
• sometimes the hemming area in general

Itu usually means that, but in Malay it is also often used to mark something as specific or already known in the context.

So kelim itu can mean:

• that hem
• the hem (the specific one being talked about)

This is very common in Malay. A word like itu does not always sound as strongly demonstrative as English that. Sometimes it functions more like a definiteness marker.

Compare:

• kelim = a hem / hem in general
• kelim itu = that hem / the specific hem

Kalau-kalau is a fixed expression meaning in case or just in case.

It is not simply kalau repeated randomly. In Malay, repetition can create a slightly different meaning, and kalau-kalau has become an established phrase used for precaution.

So here it gives the idea:

• I’m doing this as a precaution
• just in case the stitching is loose

It has a more cautious feeling than plain kalau.

A useful way to think about it is:

• kalau = if
• kalau-kalau = just in case / in case

Examples:

• Kalau hujan, saya tak pergi.
  If it rains, I’m not going.
• Saya bawa payung kalau-kalau hujan.
  I brought an umbrella just in case it rains.

In your sentence, kalau-kalau jahitannya longgar means the speaker is taking preventive action.

Jahitannya comes from jahitan + -nya.

• jahit = sew / sewing
• jahitan = stitching, sewing, sewn part, seam
• jahitannya = its stitching, the stitching, or the seam/stitches

In this sentence, it most naturally means the stitching or its stitching.

The suffix -nya can do several jobs in Malay. Here it most likely gives a sense like:

• its stitching
• the stitching

So jahitannya longgar means the stitching is loose or its stitching is loose.

In this sentence, -nya most likely refers back to the item being discussed, so it can be understood as its.

So:

• jahitan = stitching
• jahitannya = its stitching / the stitching

Malay -nya is very flexible. It can mean things like:

• his/her/its
• the
• something already understood from context

That is why jahitannya can be translated in more than one natural way:

• its stitching
• the stitching
• the seams/stitches, depending on context

Because Malay usually does not use a verb meaning to be in sentences like this.

So:

• jahitannya longgar literally looks like its stitching loose
• but it means its stitching is loose

This is very normal in Malay.

Other examples:

• Dia tinggi. = He/She is tall.
• Bilik itu besar. = That room is big.

So in Malay, adjective sentences often work without any separate word for is.

Longgar means loose, not tight, or not firmly attached.

In a sewing context, it can describe:

• loose stitching
• a seam that is not secure
• something not tightly fastened

So jahitannya longgar suggests that the stitches may not be holding firmly.

The sentence breaks down like this:

• Saya = subject = I
• menyemat = verb = pin / fasten
• kelim itu = object = that hem / the hem
• kalau-kalau jahitannya longgar = precaution clause = in case the stitching is loose

So the overall structure is:

Subject + Verb + Object + reason/precaution clause

A very natural English pattern would be:

• I pin the hem just in case the stitching is loose.

Malay nouns usually do not have to show singular vs plural as clearly as English nouns do.

So jahitan could be understood as:

• stitching
• stitches
• seam
• sewing

The exact English choice depends on context.

In this sentence, English speakers might translate it as:

• the stitching is loose
• the stitches are loose

Both can fit the Malay.

Yes, a comma is possible in writing, especially if you want to mark a pause:

• Saya menyemat kelim itu, kalau-kalau jahitannya longgar.

But Malay punctuation is often lighter than English punctuation, and many writers would also write it without a comma:

• Saya menyemat kelim itu kalau-kalau jahitannya longgar.

Both are acceptable. The version without a comma is perfectly normal.