I tried like this but I am getting the same error. My DB has fields id, username, email. ID is set as primary key so I think you can omit it when you are inserting new values.
<cfset request.pageTitle = "Registration">
<cfif CGI.REQUEST_METHOD EQ "POST">
<!--- Check if the form fields are defined --->
<cfif IsDefined("form.username") and IsDefined("form.email")>
<!--- Establish Connection to SQLite Database --->
<cftry>
<cfquery name="insertUser" datasource="mySQLiteDB">
INSERT INTO users (username, email)
VALUES (
<cfqueryparam value="#form.username#" cfsqltype="CF_SQL_VARCHAR">,
<cfqueryparam value="#form.email#" cfsqltype="CF_SQL_VARCHAR">
)
</cfquery>
<!--- Check if the registration was successful --->
<cfif insertUser.recordCount>
<p class="style1">Registration successful!</p>
<cfelse>
<p class="style1">Registration failed. Please try again.</p>
</cfif>
<cfcatch type="database">
<p class="style1">Database error occurred: #cfcatch.message#</p>
</cfcatch>
</cftry>
<cfelse>
<p class="style1">Form fields are not defined.</p>
</cfif>
</cfif>
<p align="center" class="style2">REGISTRATION FORM</p>
<p class="style1">In Development process</p>
<div class="reg__container">
<form class="form__container" method="post">
<label class="form-label" for="username">Username:</label>
<input class="form-input" type="text" id="username" name="username" placeholder="Enter your username" required>
<label class="form-label" for="email">Email:</label>
<input class="form-input" type="email" id="email" name="email" placeholder="Enter your email" required>
<div class="form-checkbox-container">
<input class="form-checkbox" type="checkbox" id="subscribe" name="subscribe">
<label class="form-label" for="subscribe">Agree to our <a href="#">terms</a> of use.</label>
</div>
<button class="form-button" type="submit">Submit</button>
</form>
</div>