Al principio, me sentí inseguro en la clase de español.

Al principio means at the beginning or at first. It talks about the start of a situation or time period.

In this sentence, Al principio tells us that this feeling happened at the beginning of the Spanish class experience.

En principio is different. It usually means in principle, theoretically, or for now, based on the current plan.

• Al principio, me sentí inseguro. = At first, I felt insecure.
• En principio, voy a ir. = In principle / For now, I’m going to go.

So for time sequence, al principio is the correct choice here.

Because the verb here is sentirse, which means to feel in the sense of someone’s emotional or personal state.

• sentir = to feel, to feel something
• sentirse = to feel a certain way

Compare:

• Sentí frío. = I felt cold.
• Me sentí inseguro. = I felt insecure.

The me is the reflexive pronoun that goes with sentirse for I.

Full pattern:

• me siento = I feel
• te sientes = you feel
• se siente = he/she feels
• nos sentimos = we feel
• se sienten = they feel

Sentí is the preterite, which is often used for a completed feeling or reaction at a specific time.

Here, the speaker is looking back and saying that at the beginning, they felt insecure. It presents that feeling as part of a completed past situation.

Sentía is the imperfect, which would emphasize an ongoing or habitual state in the past.

Compare:

• Al principio, me sentí inseguro. = At first, I felt insecure.
  This sounds like a past reaction or state viewed as a whole.

• Al principio, me sentía inseguro. = At first, I used to feel / was feeling insecure.
  This puts more focus on the ongoing nature of the feeling.

Both can be possible in some contexts, but me sentí is very natural if the speaker is summarizing how they felt at that stage.

The infinitive is sentirse in this sentence.

That matters because sentí by itself comes from sentir, but the meaning here requires the reflexive form:

• sentir = to feel something
• sentirse = to feel a certain way

So me sentí = I felt

Inseguro agrees with the person being described.

If the speaker is male, you use:

• me sentí inseguro

If the speaker is female, you use:

• me sentí insegura

This is because adjectives in Spanish often change for gender when describing people.

• masculine singular: inseguro
• feminine singular: insegura

Yes, but the meaning shifts a little.

• Me sentí inseguro = I felt insecure
  This focuses on the personal feeling or emotional experience.

• Estaba inseguro = I was insecure / I was unsure
  This can describe a state more generally and can sometimes also mean uncertain, depending on context.

In this sentence, me sentí inseguro sounds very natural because it emphasizes how the person felt emotionally in the class.

In a normal conjugated verb form, object and reflexive pronouns usually go before the verb.

So:

• me sentí
• te sentiste
• se sintió

With infinitives or gerunds, pronouns can attach to the end:

• Voy a sentirme mejor.
• Estoy sintiéndome mejor.

But with a simple past tense verb like sentí, the pronoun goes before it:

• me sentí

Here, en la clase de español means something like in Spanish class or in the Spanish class.

It can refer to the setting where the feeling happened. In English, we might translate it as:

• in Spanish class
• during Spanish class

Literally, it is:

• en = in
• la clase de español = the Spanish class / the Spanish lesson

So it locates the experience in that classroom or class situation.

Because clase de español means Spanish class in the sense of a class about the Spanish language.

In Spanish, de + subject is very common for school subjects:

• clase de español = Spanish class
• clase de matemáticas = math class
• clase de historia = history class

If you said clase española, it would more likely mean a Spanish class in the sense of a class that is Spanish in origin or style, which is not the intended meaning here.

Yes. The accent mark in sentí shows the correct stress pattern and also helps distinguish the written form.

Sentí is the yo form of the preterite:

• yo sentí = I felt

Without the accent, senti would not be standard Spanish spelling.

The accent tells you the stress falls on the last syllable: sen-TÍ.

You would say:

Al principio, nos sentimos inseguros en la clase de español.

Changes:

• me → nos
• sentí → sentimos
• inseguro → inseguros if the group is masculine or mixed
• inseguras if the group is all female

Examples:

• Al principio, nos sentimos inseguros...
• Al principio, nos sentimos inseguras...

Yes. Inseguro can mean both, depending on context.

In this sentence, it most naturally means insecure, especially emotionally or socially.

But in other contexts, it can mean unsure or uncertain:

• Estoy inseguro de mi respuesta. = I’m unsure about my answer.

So context tells you whether it means emotional insecurity or uncertainty. Here, because it’s about being in Spanish class at the beginning, insecure is the best fit.